diff --git a/.phpcs.xml.dist b/.phpcs.xml.dist
index 3eafb6ca1..ba381a28f 100644
--- a/.phpcs.xml.dist
+++ b/.phpcs.xml.dist
@@ -5,6 +5,7 @@
     <file>samples</file>
     <file>src</file>
     <file>tests</file>
+    <file>infra</file>
 
     <exclude-pattern>samples/Header.php</exclude-pattern>
     <exclude-pattern>*/tests/Core/*/*Test\.(inc|css|js)$</exclude-pattern>
diff --git a/infra/DocumentGenerator.php b/infra/DocumentGenerator.php
index e2c3c86cb..5a86d1778 100644
--- a/infra/DocumentGenerator.php
+++ b/infra/DocumentGenerator.php
@@ -52,7 +52,7 @@ class DocumentGenerator
         return rtrim($result, ' ');
     }
 
-    private static function getPhpSpreadsheetFunctionText($functionCall): string
+    private static function getPhpSpreadsheetFunctionText(mixed $functionCall): string
     {
         if (is_string($functionCall)) {
             return $functionCall;
diff --git a/infra/LocaleGenerator.php b/infra/LocaleGenerator.php
index 5e570f7f0..508a6480e 100644
--- a/infra/LocaleGenerator.php
+++ b/infra/LocaleGenerator.php
@@ -38,32 +38,32 @@ class LocaleGenerator
      */
     protected $translationBaseFolder;
 
-    protected $phpSpreadsheetFunctions;
+    protected array $phpSpreadsheetFunctions;
 
     /**
      * @var Spreadsheet
      */
     protected $translationSpreadsheet;
 
-    protected $verbose;
+    protected bool $verbose;
 
     /**
      * @var Worksheet
      */
     protected $localeTranslations;
 
-    protected $localeLanguageMap = [];
+    protected array $localeLanguageMap = [];
 
-    protected $errorCodeMap = [];
+    protected array $errorCodeMap = [];
 
     /**
      * @var Worksheet
      */
     private $functionNameTranslations;
 
-    protected $functionNameLanguageMap = [];
+    protected array $functionNameLanguageMap = [];
 
-    protected $functionNameMap = [];
+    protected array $functionNameMap = [];
 
     public function __construct(
         string $translationBaseFolder,
@@ -98,7 +98,7 @@ class LocaleGenerator
         }
     }
 
-    protected function buildConfigFileForLocale($column, $locale): void
+    protected function buildConfigFileForLocale(string $column, string $locale): void
     {
         $language = $this->localeTranslations->getCell($column . self::ENGLISH_LANGUAGE_NAME_ROW)->getValue();
         $localeLanguage = $this->localeTranslations->getCell($column . self::LOCALE_LANGUAGE_NAME_ROW)->getValue();
@@ -124,7 +124,8 @@ class LocaleGenerator
         fclose($configFile);
     }
 
-    protected function writeConfigArgumentSeparator($configFile, $column): void
+    /** @param resource $configFile resource to write to */
+    protected function writeConfigArgumentSeparator($configFile, string $column): void
     {
         $translationCell = $this->localeTranslations->getCell($column . self::ARGUMENT_SEPARATOR_ROW);
         $localeValue = $translationCell->getValue();
@@ -136,7 +137,8 @@ class LocaleGenerator
         }
     }
 
-    protected function writeConfigCurrencySymbol($configFile, $column): void
+    /** @param resource $configFile resource to write to */
+    protected function writeConfigCurrencySymbol($configFile, string $column): void
     {
         $translationCell = $this->localeTranslations->getCell($column . self::CURRENCY_SYMBOL_ROW);
         $localeValue = $translationCell->getValue();
@@ -151,7 +153,7 @@ class LocaleGenerator
         }
     }
 
-    protected function buildFunctionsFileForLocale($column, $locale): void
+    protected function buildFunctionsFileForLocale(string $column, string $locale): void
     {
         $language = $this->functionNameTranslations->getCell($column . self::ENGLISH_LANGUAGE_NAME_ROW)->getValue();
         $localeLanguage = $this->functionNameTranslations->getCell($column . self::LOCALE_LANGUAGE_NAME_ROW)
@@ -176,6 +178,7 @@ class LocaleGenerator
         fclose($functionFile);
     }
 
+    /** @return resource used by other methods in this class */
     protected function openConfigFile(string $locale, string $language, string $localeLanguage)
     {
         $this->log("Building locale {$locale} ($language) configuration");
@@ -185,11 +188,15 @@ class LocaleGenerator
         $this->log("Writing locale configuration to {$configFileName}");
 
         $configFile = fopen($configFileName, 'wb');
+        if ($configFile === false) {
+            throw new Exception('Unable to open $configFileName for write');
+        }
         $this->writeFileHeader($configFile, $localeLanguage, $language, 'locale settings');
 
         return $configFile;
     }
 
+    /** @return resource used by other methods in this class */
     protected function openFunctionNameFile(string $locale, string $language, string $localeLanguage)
     {
         $this->log("Building locale {$locale} ($language) function names");
@@ -199,6 +206,9 @@ class LocaleGenerator
         $this->log("Writing local function names to {$functionFileName}");
 
         $functionFile = fopen($functionFileName, 'wb');
+        if ($functionFile === false) {
+            throw new Exception('Unable to open $functionFileName for write');
+        }
         $this->writeFileHeader($functionFile, $localeLanguage, $language, 'function name translations');
 
         return $functionFile;
@@ -218,6 +228,7 @@ class LocaleGenerator
         return $localeFolder;
     }
 
+    /** @param resource $localeFile file being written to */
     protected function writeFileHeader($localeFile, string $localeLanguage, string $language, string $title): void
     {
         fwrite($localeFile, str_repeat('#', 60) . self::EOL);
@@ -229,6 +240,7 @@ class LocaleGenerator
         fwrite($localeFile, str_repeat('#', 60) . self::EOL . self::EOL);
     }
 
+    /** @param resource $localeFile file being written to */
     protected function writeFileSectionHeader($localeFile, string $header): void
     {
         fwrite($localeFile, self::EOL . '##' . self::EOL);
@@ -245,9 +257,6 @@ class LocaleGenerator
     protected function getTranslationSheet(string $sheetName): Worksheet
     {
         $worksheet = $this->translationSpreadsheet->setActiveSheetIndexByName($sheetName);
-        if ($worksheet === null) {
-            throw new Exception("{$sheetName} Worksheet not found");
-        }
 
         return $worksheet;
     }
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index f6ce123ad..154541708 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -8,6 +8,8 @@ parameters:
     paths:
         - src/
         - tests/
+        - samples/
+        - infra/
     excludePaths:
         - src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
         - src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php
@@ -21,3 +23,4 @@ parameters:
     ignoreErrors:
         # Accept a bit anything for assert methods
         - '~^Parameter \#2 .* of static method PHPUnit\\Framework\\Assert\:\:assert\w+\(\) expects .*, .* given\.$~'
+        - '~^Variable \$helper might not be defined\.$~'
diff --git a/samples/Autofilter/10_Autofilter_selection_2.php b/samples/Autofilter/10_Autofilter_selection_2.php
index 4d5d891cf..6b82bcdf5 100644
--- a/samples/Autofilter/10_Autofilter_selection_2.php
+++ b/samples/Autofilter/10_Autofilter_selection_2.php
@@ -126,7 +126,7 @@ $helper->log('Set country code filter (Column C) to "Germany"');
 $autoFilter->getColumn('D')
     ->setFilterType(Column::AUTOFILTER_FILTERTYPE_DYNAMICFILTER)
     ->createRule()
-    ->setRule(Rule::AUTOFILTER_COLUMN_RULE_EQUAL, null, Rule::AUTOFILTER_RULETYPE_DYNAMIC_YEARTODATE)
+    ->setRule(Rule::AUTOFILTER_COLUMN_RULE_EQUAL, '', Rule::AUTOFILTER_RULETYPE_DYNAMIC_YEARTODATE)
     ->setRuleType(Rule::AUTOFILTER_RULETYPE_DYNAMICFILTER);
 
 $helper->log('Add filter on the Date (Column D) to display year to date');
diff --git a/samples/Basic/02_Types.php b/samples/Basic/02_Types.php
index 4eaaa8b15..d28af579d 100644
--- a/samples/Basic/02_Types.php
+++ b/samples/Basic/02_Types.php
@@ -109,9 +109,9 @@ $richText = new RichText();
 $richText->createText('你好 ');
 
 $payable = $richText->createTextRun('你 好 吗？');
-$payable->getFont()->setBold(true);
-$payable->getFont()->setItalic(true);
-$payable->getFont()->setColor(new Color(Color::COLOR_DARKGREEN));
+$payable->getFontOrThrow()->setBold(true);
+$payable->getFontOrThrow()->setItalic(true);
+$payable->getFontOrThrow()->setColor(new Color(Color::COLOR_DARKGREEN));
 
 $richText->createText(', unless specified otherwise on the invoice.');
 
@@ -123,7 +123,7 @@ $richText2 = new RichText();
 $richText2->createText("black text\n");
 
 $red = $richText2->createTextRun('red text');
-$red->getFont()->setColor(new Color(Color::COLOR_RED));
+$red->getFontOrThrow()->setColor(new Color(Color::COLOR_RED));
 
 $spreadsheet->getActiveSheet()
     ->getCell('C14')
diff --git a/samples/Basic/19_Namedrange.php b/samples/Basic/19_Namedrange.php
index 6170fa28e..5b1a25270 100644
--- a/samples/Basic/19_Namedrange.php
+++ b/samples/Basic/19_Namedrange.php
@@ -36,6 +36,9 @@ $spreadsheet->addNamedRange(new NamedRange('PersonLN', $spreadsheet->getActiveSh
 
 // Rename named ranges
 $helper->log('Rename named ranges');
+if ($spreadsheet->getNamedRange('PersonName') === null) {
+    throw new Exception('named range not found');
+}
 $spreadsheet->getNamedRange('PersonName')->setName('PersonFN');
 
 // Rename worksheet
diff --git a/samples/Basic/25_In_memory_image.php b/samples/Basic/25_In_memory_image.php
index 1833e683a..7ba4871b3 100644
--- a/samples/Basic/25_In_memory_image.php
+++ b/samples/Basic/25_In_memory_image.php
@@ -27,12 +27,15 @@ $spreadsheet->getProperties()->setCreator('Maarten Balliauw')
 
 // Generate an image
 $helper->log('Generate an image');
-$gdImage = @imagecreatetruecolor(120, 20);
+$gdImage = imagecreatetruecolor(120, 20);
 if (!$gdImage) {
-    exit('Cannot Initialize new GD image stream');
+    throw new Exception('Cannot Initialize new GD image stream');
 }
 
 $textColor = imagecolorallocate($gdImage, 255, 255, 255);
+if ($textColor === false) {
+    throw new Exception('imagecolorallocate failed');
+}
 imagestring($gdImage, 1, 5, 5, 'Created with PhpSpreadsheet', $textColor);
 
 // Add a drawing to the worksheet
diff --git a/samples/Basic/39_Dropdown.php b/samples/Basic/39_Dropdown.php
index 0e8ff52b6..232ed0eda 100644
--- a/samples/Basic/39_Dropdown.php
+++ b/samples/Basic/39_Dropdown.php
@@ -20,7 +20,8 @@ $spreadsheet->getProperties()
     ->setDescription('Test document for PhpSpreadsheet, generated using PHP classes.')
     ->setKeywords('Office PhpSpreadsheet php')
     ->setCategory('Test result file');
-function transpose($value)
+
+function transpose(string $value): array
 {
     return [$value];
 }
@@ -30,12 +31,12 @@ $continentColumn = 'D';
 $column = 'F';
 
 // Set data for dropdowns
-$continents = glob(__DIR__ . '/data/continents/*');
+$continents = glob(__DIR__ . '/data/continents/*') ?: [];
 foreach ($continents as $key => $filename) {
     $continent = pathinfo($filename, PATHINFO_FILENAME);
     $helper->log("Loading $continent");
     $continent = str_replace(' ', '_', $continent);
-    $countries = file($filename, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+    $countries = file($filename, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES) ?: [];
     $countryCount = count($countries);
 
     // Transpose $countries from a row to a column array
diff --git a/samples/Calculations/Engineering/Convert-Online.php b/samples/Calculations/Engineering/Convert-Online.php
index e20e4c79b..3d26a3f6b 100644
--- a/samples/Calculations/Engineering/Convert-Online.php
+++ b/samples/Calculations/Engineering/Convert-Online.php
@@ -77,6 +77,7 @@ if (isset($_POST['submit'])) {
     $quantity = $_POST['quantity'];
     $fromUnit = $_POST['fromUnit'];
     $toUnit = $_POST['toUnit'];
+    /** @var float|string */
     $result = ConvertUOM::CONVERT($quantity, $fromUnit, $toUnit);
 
     echo "{$quantity} {$units[$_POST['category']][$fromUnit]} is {$result} {$units[$_POST['category']][$toUnit]}", PHP_EOL;
diff --git a/samples/Chart/32_Chart_read_write.php b/samples/Chart/32_Chart_read_write.php
index 42944c0cc..900c9567c 100644
--- a/samples/Chart/32_Chart_read_write.php
+++ b/samples/Chart/32_Chart_read_write.php
@@ -13,7 +13,7 @@ if ((isset($argc)) && ($argc > 1)) {
         $inputFileNames[] = __DIR__ . '/../templates/' . $argv[$i];
     }
 } else {
-    $inputFileNames = glob($inputFileNames);
+    $inputFileNames = glob($inputFileNames) ?: [];
 }
 foreach ($inputFileNames as $inputFileName) {
     $inputFileNameShort = basename($inputFileName);
@@ -40,7 +40,7 @@ foreach ($inputFileNames as $inputFileName) {
         } else {
             natsort($chartNames);
             foreach ($chartNames as $i => $chartName) {
-                $chart = $worksheet->getChartByName($chartName);
+                $chart = $worksheet->getChartByNameOrThrow($chartName);
                 if ($chart->getTitle() !== null) {
                     $caption = '"' . $chart->getTitle()->getCaptionText($spreadsheet) . '"';
                 } else {
@@ -48,15 +48,15 @@ foreach ($inputFileNames as $inputFileName) {
                 }
                 $helper->log('    ' . $chartName . ' - ' . $caption);
                 $indentation = str_repeat(' ', strlen($chartName) + 3);
-                $groupCount = $chart->getPlotArea()->getPlotGroupCount();
+                $groupCount = $chart->getPlotAreaOrThrow()->getPlotGroupCount();
                 if ($groupCount == 1) {
-                    $chartType = $chart->getPlotArea()->getPlotGroupByIndex(0)->getPlotType();
+                    $chartType = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex(0)->getPlotType();
                     $helper->log($indentation . '    ' . $chartType);
                     $helper->renderChart($chart, __FILE__);
                 } else {
                     $chartTypes = [];
                     for ($i = 0; $i < $groupCount; ++$i) {
-                        $chartTypes[] = $chart->getPlotArea()->getPlotGroupByIndex($i)->getPlotType();
+                        $chartTypes[] = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex($i)->getPlotType();
                     }
                     $chartTypes = array_unique($chartTypes);
                     if (count($chartTypes) == 1) {
diff --git a/samples/Chart/32_Chart_read_write_HTML.php b/samples/Chart/32_Chart_read_write_HTML.php
index 3cb377873..0dc5484ce 100644
--- a/samples/Chart/32_Chart_read_write_HTML.php
+++ b/samples/Chart/32_Chart_read_write_HTML.php
@@ -18,7 +18,7 @@ if ((isset($argc)) && ($argc > 1)) {
         $inputFileNames[] = __DIR__ . '/../templates/' . $argv[$i];
     }
 } else {
-    $inputFileNames = glob($inputFileNames);
+    $inputFileNames = glob($inputFileNames) ?: [];
 }
 foreach ($inputFileNames as $inputFileName) {
     $inputFileNameShort = basename($inputFileName);
@@ -46,22 +46,22 @@ foreach ($inputFileNames as $inputFileName) {
         } else {
             natsort($chartNames);
             foreach ($chartNames as $i => $chartName) {
-                $chart = $worksheet->getChartByName($chartName);
+                $chart = $worksheet->getChartByNameOrThrow($chartName);
                 if ($chart->getTitle() !== null) {
-                    $caption = '"' . implode(' ', $chart->getTitle()->getCaption()) . '"';
+                    $caption = '"' . $chart->getTitle()->getCaptionText($spreadsheet) . '"';
                 } else {
                     $caption = 'Untitled';
                 }
                 $helper->log('    ' . $chartName . ' - ' . $caption);
                 $helper->log(str_repeat(' ', strlen($chartName) + 3));
-                $groupCount = $chart->getPlotArea()->getPlotGroupCount();
+                $groupCount = $chart->getPlotAreaOrThrow()->getPlotGroupCount();
                 if ($groupCount == 1) {
-                    $chartType = $chart->getPlotArea()->getPlotGroupByIndex(0)->getPlotType();
+                    $chartType = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex(0)->getPlotType();
                     $helper->log('    ' . $chartType);
                 } else {
                     $chartTypes = [];
                     for ($i = 0; $i < $groupCount; ++$i) {
-                        $chartTypes[] = $chart->getPlotArea()->getPlotGroupByIndex($i)->getPlotType();
+                        $chartTypes[] = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex($i)->getPlotType();
                     }
                     $chartTypes = array_unique($chartTypes);
                     if (count($chartTypes) == 1) {
diff --git a/samples/Chart/32_Chart_read_write_PDF.php b/samples/Chart/32_Chart_read_write_PDF.php
index e3d702a9d..0ac41f71f 100644
--- a/samples/Chart/32_Chart_read_write_PDF.php
+++ b/samples/Chart/32_Chart_read_write_PDF.php
@@ -20,7 +20,7 @@ if ((isset($argc)) && ($argc > 1)) {
         $inputFileNames[] = __DIR__ . '/../templates/' . $argv[$i];
     }
 } else {
-    $inputFileNames = glob($inputFileNames);
+    $inputFileNames = glob($inputFileNames) ?: [];
 }
 foreach ($inputFileNames as $inputFileName) {
     $inputFileNameShort = basename($inputFileName);
@@ -48,22 +48,22 @@ foreach ($inputFileNames as $inputFileName) {
         } else {
             natsort($chartNames);
             foreach ($chartNames as $i => $chartName) {
-                $chart = $worksheet->getChartByName($chartName);
+                $chart = $worksheet->getChartByNameOrThrow($chartName);
                 if ($chart->getTitle() !== null) {
-                    $caption = '"' . implode(' ', $chart->getTitle()->getCaption()) . '"';
+                    $caption = '"' . $chart->getTitle()->getCaptionText($spreadsheet) . '"';
                 } else {
                     $caption = 'Untitled';
                 }
                 $helper->log('    ' . $chartName . ' - ' . $caption);
                 $helper->log(str_repeat(' ', strlen($chartName) + 3));
-                $groupCount = $chart->getPlotArea()->getPlotGroupCount();
+                $groupCount = $chart->getPlotAreaOrThrow()->getPlotGroupCount();
                 if ($groupCount == 1) {
-                    $chartType = $chart->getPlotArea()->getPlotGroupByIndex(0)->getPlotType();
+                    $chartType = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex(0)->getPlotType();
                     $helper->log('    ' . $chartType);
                 } else {
                     $chartTypes = [];
                     for ($i = 0; $i < $groupCount; ++$i) {
-                        $chartTypes[] = $chart->getPlotArea()->getPlotGroupByIndex($i)->getPlotType();
+                        $chartTypes[] = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex($i)->getPlotType();
                     }
                     $chartTypes = array_unique($chartTypes);
                     if (count($chartTypes) == 1) {
diff --git a/samples/Chart/33_Chart_create_line_dateaxis.php b/samples/Chart/33_Chart_create_line_dateaxis.php
index d7b674f6d..c177de79a 100644
--- a/samples/Chart/33_Chart_create_line_dateaxis.php
+++ b/samples/Chart/33_Chart_create_line_dateaxis.php
@@ -195,7 +195,7 @@ $spreadsheet->createSheet();
 $chartSheet = $spreadsheet->getSheet(1);
 $chartSheet->setTitle('Scatter+Line Chart');
 
-$chartSheet = $spreadsheet->getSheetByName('Scatter+Line Chart');
+$chartSheet = $spreadsheet->getSheetByNameOrThrow('Scatter+Line Chart');
 // Add the chart to the worksheet
 $chartSheet->addChart($chart);
 
@@ -340,11 +340,14 @@ $spreadsheet->disconnectWorksheets();
 
 function dateRange(int $nrows, Spreadsheet $wrkbk): array
 {
-    $dataSheet = $wrkbk->getSheetByName('Data');
+    $dataSheet = $wrkbk->getSheetByNameOrThrow('Data');
 
     // start the xaxis at the beginning of the quarter of the first date
     $startDateStr = $dataSheet->getCell('B2')->getValue(); // yyyy-mm-dd date string
     $startDate = DateTime::createFromFormat('Y-m-d', $startDateStr); // php date obj
+    if ($startDate === false) {
+        throw new Exception("invalid start date $startDateStr on spreadsheet");
+    }
 
     // get date of first day of the quarter of the start date
     $startMonth = (int) $startDate->format('n'); // suppress leading zero
@@ -357,12 +360,19 @@ function dateRange(int $nrows, Spreadsheet $wrkbk): array
     // end the xaxis at the end of the quarter of the last date
     $lastDateStr = $dataSheet->getCell([2, $nrows + 1])->getValue();
     $lastDate = DateTime::createFromFormat('Y-m-d', $lastDateStr);
+    if ($lastDate === false) {
+        throw new Exception("invalid last date $lastDateStr on spreadsheet");
+    }
     $lastMonth = (int) $lastDate->format('n');
     $lastYr = (int) $lastDate->format('Y');
     $qtr = intdiv($lastMonth, 3) + (($lastMonth % 3 > 0) ? 1 : 0);
     $qtrEndMonth = 3 + (($qtr - 1) * 3);
     $qtrEndMonth = sprintf('%02d', $qtrEndMonth);
-    $lastDOM = DateTime::createFromFormat('Y-m-d', "$lastYr-$qtrEndMonth-01")->format('t');
+    $lastDOMDate = DateTime::createFromFormat('Y-m-d', "$lastYr-$qtrEndMonth-01");
+    if ($lastDOMDate === false) {
+        throw new Exception("invalid last dom date $lastYr-$qtrEndMonth-01 on spreadsheet");
+    }
+    $lastDOM = $lastDOMDate->format('t');
     $qtrEndStr = "$lastYr-$qtrEndMonth-$lastDOM";
     $ExcelQtrEndDateVal = SharedDate::convertIsoDate($qtrEndStr);
 
diff --git a/samples/Chart/33_Chart_create_scatter5_trendlines.php b/samples/Chart/33_Chart_create_scatter5_trendlines.php
index f58aadaf7..7467c8206 100644
--- a/samples/Chart/33_Chart_create_scatter5_trendlines.php
+++ b/samples/Chart/33_Chart_create_scatter5_trendlines.php
@@ -169,7 +169,7 @@ $spreadsheet->createSheet();
 $chartSheet = $spreadsheet->getSheet(1);
 $chartSheet->setTitle('Scatter Chart');
 
-$chartSheet = $spreadsheet->getSheetByName('Scatter Chart');
+$chartSheet = $spreadsheet->getSheetByNameOrThrow('Scatter Chart');
 // Add the chart to the worksheet
 $chartSheet->addChart($chart);
 
diff --git a/samples/Chart/35_Chart_render.php b/samples/Chart/35_Chart_render.php
index 4c403d993..57eb691ef 100644
--- a/samples/Chart/35_Chart_render.php
+++ b/samples/Chart/35_Chart_render.php
@@ -19,11 +19,13 @@ if ((isset($argc)) && ($argc > 1)) {
         $inputFileNames[] = __DIR__ . '/../templates/' . $argv[$i];
     }
 } else {
-    $inputFileNames = glob($inputFileNames);
+    $inputFileNames = glob($inputFileNames) ?: [];
 }
 if (count($inputFileNames) === 1) {
+    /** @var string[] */
     $unresolvedErrors = [];
 } else {
+    /** @var string[] */
     $unresolvedErrors = [
         // The following spreadsheet was created by 3rd party software,
         // and doesn't include the data that usually accompanies a chart.
@@ -66,9 +68,9 @@ foreach ($inputFileNames as $inputFileName) {
             natsort($chartNames);
             foreach ($chartNames as $j => $chartName) {
                 $i = $renderedCharts + $j;
-                $chart = $worksheet->getChartByName($chartName);
+                $chart = $worksheet->getChartByNameOrThrow($chartName);
                 if ($chart->getTitle() !== null) {
-                    $caption = '"' . implode(' ', $chart->getTitle()->getCaption()) . '"';
+                    $caption = '"' . $chart->getTitle()->getCaptionText($spreadsheet) . '"';
                 } else {
                     $caption = 'Untitled';
                 }
diff --git a/samples/Chart/35_Chart_render33.php b/samples/Chart/35_Chart_render33.php
index 97091fcee..f9c7c11ad 100644
--- a/samples/Chart/35_Chart_render33.php
+++ b/samples/Chart/35_Chart_render33.php
@@ -10,7 +10,7 @@ require __DIR__ . '/../Header.php';
 Settings::setChartRenderer(\PhpOffice\PhpSpreadsheet\Chart\Renderer\MtJpGraphRenderer::class);
 
 $inputFileType = 'Xlsx';
-$inputFileNames = $helper->getTemporaryFolder() . '/33_Chart_create_*.xlsx';
+$inputFileNamesString = $helper->getTemporaryFolder() . '/33_Chart_create_*.xlsx';
 
 if ((isset($argc)) && ($argc > 1)) {
     $inputFileNames = [];
@@ -18,11 +18,13 @@ if ((isset($argc)) && ($argc > 1)) {
         $inputFileNames[] = __DIR__ . '/../templates/' . $argv[$i];
     }
 } else {
-    $inputFileNames = glob($inputFileNames);
+    $inputFileNames = glob($inputFileNamesString) ?: [];
 }
 if (count($inputFileNames) === 1) {
+    /** @var string[] */
     $unresolvedErrors = [];
 } else {
+    /** @var string[] */
     $unresolvedErrors = [
         //'33_Chart_create_bar_stacked.xlsx', // fixed with mitoteam/jpgraph 10.3
     ];
@@ -62,9 +64,9 @@ foreach ($inputFileNames as $inputFileName) {
             natsort($chartNames);
             foreach ($chartNames as $j => $chartName) {
                 $i = $renderedCharts + $j;
-                $chart = $worksheet->getChartByName($chartName);
+                $chart = $worksheet->getChartByNameOrThrow($chartName);
                 if ($chart->getTitle() !== null) {
-                    $caption = '"' . implode(' ', $chart->getTitle()->getCaption()) . '"';
+                    $caption = '"' . $chart->getTitle()->getCaptionText($spreadsheet) . '"';
                 } else {
                     $caption = 'Untitled';
                 }
diff --git a/samples/Chart/37_Chart_dynamic_title.php b/samples/Chart/37_Chart_dynamic_title.php
index b8b801faa..e0df17cd0 100644
--- a/samples/Chart/37_Chart_dynamic_title.php
+++ b/samples/Chart/37_Chart_dynamic_title.php
@@ -37,7 +37,7 @@ foreach ($inputFileNames as $inputFileName) {
         } else {
             natsort($chartNames);
             foreach ($chartNames as $i => $chartName) {
-                $chart = $worksheet->getChartByName($chartName);
+                $chart = $worksheet->getChartByNameOrThrow($chartName);
                 if ($chart->getTitle() !== null) {
                     $caption = '"' . $chart->getTitle()->getCaptionText($spreadsheet) . '"';
                 } else {
@@ -45,15 +45,15 @@ foreach ($inputFileNames as $inputFileName) {
                 }
                 $helper->log('    ' . $chartName . ' - ' . $caption);
                 $indentation = str_repeat(' ', strlen($chartName) + 3);
-                $groupCount = $chart->getPlotArea()->getPlotGroupCount();
+                $groupCount = $chart->getPlotAreaOrThrow()->getPlotGroupCount();
                 if ($groupCount == 1) {
-                    $chartType = $chart->getPlotArea()->getPlotGroupByIndex(0)->getPlotType();
+                    $chartType = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex(0)->getPlotType();
                     $helper->log($indentation . '    ' . $chartType);
                     $helper->renderChart($chart, __FILE__, $spreadsheet);
                 } else {
                     $chartTypes = [];
                     for ($i = 0; $i < $groupCount; ++$i) {
-                        $chartTypes[] = $chart->getPlotArea()->getPlotGroupByIndex($i)->getPlotType();
+                        $chartTypes[] = $chart->getPlotAreaOrThrow()->getPlotGroupByIndex($i)->getPlotType();
                     }
                     $chartTypes = array_unique($chartTypes);
                     if (count($chartTypes) == 1) {
diff --git a/samples/DefinedNames/CrossWorksheetNamedFormula.php b/samples/DefinedNames/CrossWorksheetNamedFormula.php
index 5ce765162..6c2faec2b 100644
--- a/samples/DefinedNames/CrossWorksheetNamedFormula.php
+++ b/samples/DefinedNames/CrossWorksheetNamedFormula.php
@@ -40,7 +40,7 @@ setYearlyData($worksheet, '2020', $data2020);
 $worksheet = $spreadsheet->addSheet(new Worksheet($spreadsheet));
 setYearlyData($worksheet, '2020', [], 'GROWTH');
 
-function setYearlyData(Worksheet $worksheet, string $year, $yearlyData, ?string $title = null): void
+function setYearlyData(Worksheet $worksheet, string $year, array $yearlyData, ?string $title = null): void
 {
     // Set up some basic data
     $worksheetTitle = $title ?: $year;
diff --git a/samples/DefinedNames/ScopedNamedRange.php b/samples/DefinedNames/ScopedNamedRange.php
index aa71454df..88bc62777 100644
--- a/samples/DefinedNames/ScopedNamedRange.php
+++ b/samples/DefinedNames/ScopedNamedRange.php
@@ -60,12 +60,18 @@ $worksheet
     ->setCellValue("B{$row}", '=SUM(COLUMN_DATA_VALUES)')
     ->setCellValue("C{$row}", '=SUM(COLUMN_DATA_VALUES)');
 
+$range = $spreadsheet->getNamedRange('CHARGE_RATE');
+if ($range === null || $range->getWorksheet() === null) {
+    throw new Exception('expected named range not found');
+}
+$chargeRateCellValue = $spreadsheet
+    ->getSheetByNameOrThrow($range->getWorksheet()->getTitle())
+    ->getCell($range->getCellsInRange()[0])->getValue();
+
 $helper->log(sprintf(
     'Worked %.2f hours at a rate of %s - Charge to the client is %.2f',
     $worksheet->getCell("B{$row}")->getCalculatedValue(),
-    $chargeRateCellValue = $spreadsheet
-        ->getSheetByName($spreadsheet->getNamedRange('CHARGE_RATE')->getWorksheet()->getTitle())
-        ->getCell($spreadsheet->getNamedRange('CHARGE_RATE')->getCellsInRange()[0])->getValue(),
+    $chargeRateCellValue,
     $worksheet->getCell("C{$row}")->getCalculatedValue()
 ));
 
diff --git a/samples/Pdf/21b_Pdf.php b/samples/Pdf/21b_Pdf.php
index d7a1cb51e..38ba4d9c4 100644
--- a/samples/Pdf/21b_Pdf.php
+++ b/samples/Pdf/21b_Pdf.php
@@ -21,7 +21,7 @@ function replaceBody(string $html): string
         </body>
         EOF;
 
-    return preg_replace($bodystring, $bodyrepl, $html);
+    return preg_replace($bodystring, $bodyrepl, $html) ?? '';
 }
 
 require __DIR__ . '/../Header.php';
diff --git a/samples/Pdf/21c_Pdf.php b/samples/Pdf/21c_Pdf.php
index f556dcb2f..6b6e6ab05 100644
--- a/samples/Pdf/21c_Pdf.php
+++ b/samples/Pdf/21c_Pdf.php
@@ -16,7 +16,7 @@ function addHeadersFootersMpdf2000(string $html): string
         odd-footer-name: html_myFooter2;
 
         EOF;
-    $html = preg_replace('/@page page0 {/', $pagerepl, $html);
+    $html = preg_replace('/@page page0 {/', $pagerepl, $html) ?? '';
     $bodystring = '/<body>/';
     $simulatedBodyStart = Mpdf::SIMULATED_BODY_START;
     $bodyrepl = <<<EOF
@@ -40,7 +40,7 @@ function addHeadersFootersMpdf2000(string $html): string
 
         EOF;
 
-    return preg_replace($bodystring, $bodyrepl, $html);
+    return preg_replace($bodystring, $bodyrepl, $html) ?? '';
 }
 
 $spreadsheet = new Spreadsheet();
diff --git a/samples/Pdf/21e_UnusualFont_mpdf.php b/samples/Pdf/21e_UnusualFont_mpdf.php
index 2485cb65d..36619d704 100644
--- a/samples/Pdf/21e_UnusualFont_mpdf.php
+++ b/samples/Pdf/21e_UnusualFont_mpdf.php
@@ -4,7 +4,7 @@ use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PhpOffice\PhpSpreadsheet\Writer\Pdf\Mpdf2;
 
 require __DIR__ . '/../Header.php';
-require_once __DIR__ . '/mpdf2.inc';
+require_once __DIR__ . '/Mpdf2.php';
 
 $spreadsheet = new Spreadsheet();
 
diff --git a/samples/Pdf/mpdf2.inc b/samples/Pdf/Mpdf2.php
similarity index 95%
rename from samples/Pdf/mpdf2.inc
rename to samples/Pdf/Mpdf2.php
index 749bcd01e..1b7ed8a35 100644
--- a/samples/Pdf/mpdf2.inc
+++ b/samples/Pdf/Mpdf2.php
@@ -34,9 +34,9 @@ class Mpdf2 extends Mpdf
         $fontFile = 'ShadowsIntoLight-Regular.ttf';
         $config['fontdata'] = $fontdata + [ // lowercase letters only in font key
             'shadowsintolight' => [
-                    'R' => $fontFile,
-                ],
-            ];
+                'R' => $fontFile,
+            ],
+        ];
 
         return new \Mpdf\Mpdf($config);
     }
diff --git a/samples/Reader/08_Simple_file_reader_loading_several_named_worksheets.php b/samples/Reader/08_Simple_file_reader_loading_several_named_worksheets.php
index 66efc3e0f..0a79dadd9 100644
--- a/samples/Reader/08_Simple_file_reader_loading_several_named_worksheets.php
+++ b/samples/Reader/08_Simple_file_reader_loading_several_named_worksheets.php
@@ -4,9 +4,15 @@ use PhpOffice\PhpSpreadsheet\IOFactory;
 
 require __DIR__ . '/../Header.php';
 
+/** @return string[] */
+function getDesiredSheetNames(): array
+{
+    return ['Data Sheet #1', 'Data Sheet #3'];
+}
+
 $inputFileType = 'Xls';
 $inputFileName = __DIR__ . '/sampleData/example1.xls';
-$sheetnames = ['Data Sheet #1', 'Data Sheet #3'];
+$sheetnames = getDesiredSheetNames();
 
 $helper->log('Loading file ' . pathinfo($inputFileName, PATHINFO_BASENAME) . ' using IOFactory with a defined reader type of ' . $inputFileType);
 $reader = IOFactory::createReader($inputFileType);
diff --git a/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php b/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php
index 437fe6cff..a8148f33c 100644
--- a/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php
+++ b/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php
@@ -13,13 +13,13 @@ $sheetname = 'Data Sheet #3';
 
 class MyReadFilter implements IReadFilter
 {
-    private $startRow = 0;
+    private int $startRow = 0;
 
-    private $endRow = 0;
+    private int $endRow = 0;
 
-    private $columns = [];
+    private array $columns = [];
 
-    public function __construct($startRow, $endRow, $columns)
+    public function __construct(int $startRow, int $endRow, array $columns)
     {
         $this->startRow = $startRow;
         $this->endRow = $endRow;
diff --git a/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php b/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php
index ec0113261..64c5b5665 100644
--- a/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php
+++ b/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php
@@ -13,17 +13,14 @@ $inputFileName = __DIR__ . '/sampleData/example2.xls';
 /**  Define a Read Filter class implementing IReadFilter  */
 class ChunkReadFilter implements IReadFilter
 {
-    private $startRow = 0;
+    private int $startRow = 0;
 
-    private $endRow = 0;
+    private int $endRow = 0;
 
     /**
      * We expect a list of the rows that we want to read to be passed into the constructor.
-     *
-     * @param mixed $startRow
-     * @param mixed $chunkSize
      */
-    public function __construct($startRow, $chunkSize)
+    public function __construct(int $startRow, int $chunkSize)
     {
         $this->startRow = $startRow;
         $this->endRow = $startRow + $chunkSize;
diff --git a/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php b/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php
index e8c4a6590..5b2a4e48f 100644
--- a/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php
+++ b/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php
@@ -13,17 +13,14 @@ $inputFileName = __DIR__ . '/sampleData/example2.xls';
 /**  Define a Read Filter class implementing IReadFilter  */
 class ChunkReadFilter implements IReadFilter
 {
-    private $startRow = 0;
+    private int $startRow = 0;
 
-    private $endRow = 0;
+    private int $endRow = 0;
 
     /**
      * Set the list of rows that we want to read.
-     *
-     * @param mixed $startRow
-     * @param mixed $chunkSize
      */
-    public function setRows($startRow, $chunkSize): void
+    public function setRows(int $startRow, int $chunkSize): void
     {
         $this->startRow = $startRow;
         $this->endRow = $startRow + $chunkSize;
diff --git a/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php b/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php
index 82544f60a..3d6b2cb06 100644
--- a/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php
+++ b/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php
@@ -13,17 +13,14 @@ $inputFileName = __DIR__ . '/sampleData/example2.csv';
 /**  Define a Read Filter class implementing IReadFilter  */
 class ChunkReadFilter implements IReadFilter
 {
-    private $startRow = 0;
+    private int $startRow = 0;
 
-    private $endRow = 0;
+    private int $endRow = 0;
 
     /**
      * Set the list of rows that we want to read.
-     *
-     * @param mixed $startRow
-     * @param mixed $chunkSize
      */
-    public function setRows($startRow, $chunkSize): void
+    public function setRows(int $startRow, int $chunkSize): void
     {
         $this->startRow = $startRow;
         $this->endRow = $startRow + $chunkSize;
@@ -51,8 +48,8 @@ $chunkFilter = new ChunkReadFilter();
 
 // Tell the Reader that we want to use the Read Filter that we've Instantiated
 // and that we want to store it in contiguous rows/columns
-$reader->setReadFilter($chunkFilter)
-    ->setContiguous(true);
+$reader->setReadFilter($chunkFilter);
+$reader->setContiguous(true);
 
 // Instantiate a new PhpSpreadsheet object manually
 $spreadsheet = new Spreadsheet();
diff --git a/samples/Reader/20_Reader_worksheet_hyperlink_image.php b/samples/Reader/20_Reader_worksheet_hyperlink_image.php
index 2b3f294a6..19200ee21 100644
--- a/samples/Reader/20_Reader_worksheet_hyperlink_image.php
+++ b/samples/Reader/20_Reader_worksheet_hyperlink_image.php
@@ -14,9 +14,12 @@ $aSheet = $spreadsheet->getActiveSheet();
 
 $gdImage = @imagecreatetruecolor(120, 20);
 if ($gdImage === false) {
-    throw new \Exception('imagecreatetruecolor failed');
+    throw new Exception('imagecreatetruecolor failed');
 }
 $textColor = imagecolorallocate($gdImage, 255, 255, 255);
+if ($textColor === false) {
+    throw new Exception('imagecolorallocate failed');
+}
 imagestring($gdImage, 1, 5, 5, 'Created with PhpSpreadsheet', $textColor);
 
 $baseUrl = 'https://phpspreadsheet.readthedocs.io';
@@ -52,7 +55,7 @@ unlink($filename);
 $helper->log('reloaded Spreadsheet');
 
 foreach ($reloadedSpreadsheet->getActiveSheet()->getDrawingCollection() as $pDrawing) {
-    $helper->log('Read link: ' . $pDrawing->getHyperlink()->getUrl());
+    $helper->log('Read link: ' . ($pDrawing->getHyperlink()?->getUrl() ?? 'none'));
 }
 
 $helper->log('end');
diff --git a/samples/Wizards/NumberFormat/Accounting.php b/samples/Wizards/NumberFormat/Accounting.php
index c09c7ca6c..20737e502 100644
--- a/samples/Wizards/NumberFormat/Accounting.php
+++ b/samples/Wizards/NumberFormat/Accounting.php
@@ -83,11 +83,11 @@ $currencies = [
 if (isset($_POST['submit'])) {
     if (!is_numeric($_POST['number'])) {
         $helper->log('The Sample Number Value must be numeric');
-    } elseif (!is_numeric($_POST['decimals']) || str_contains($_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
+    } elseif (!is_numeric($_POST['decimals']) || str_contains((string) $_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
         $helper->log('The Decimal Places value must be positive integer');
     } else {
         try {
-            $wizard = new Wizard\Accounting($_POST['currency'], $_POST['decimals'], isset($_POST['thousands']), (bool) $_POST['position'], (bool) $_POST['spacing']);
+            $wizard = new Wizard\Accounting($_POST['currency'], (int) $_POST['decimals'], isset($_POST['thousands']), (bool) $_POST['position'], (bool) $_POST['spacing']);
             $mask = $wizard->format();
             $example = (string) NumberFormat::toFormattedString((float) $_POST['number'], $mask);
             $helper->log('<hr /><b>Code:</b><br />');
diff --git a/samples/Wizards/NumberFormat/Currency.php b/samples/Wizards/NumberFormat/Currency.php
index 87da38360..313db3194 100644
--- a/samples/Wizards/NumberFormat/Currency.php
+++ b/samples/Wizards/NumberFormat/Currency.php
@@ -83,11 +83,11 @@ $currencies = [
 if (isset($_POST['submit'])) {
     if (!is_numeric($_POST['number'])) {
         $helper->log('The Sample Number Value must be numeric');
-    } elseif (!is_numeric($_POST['decimals']) || str_contains($_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
+    } elseif (!is_numeric($_POST['decimals']) || str_contains((string) $_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
         $helper->log('The Decimal Places value must be positive integer');
     } else {
         try {
-            $wizard = new Wizard\Currency($_POST['currency'], $_POST['decimals'], isset($_POST['thousands']), (bool) $_POST['position'], (bool) $_POST['spacing']);
+            $wizard = new Wizard\Currency($_POST['currency'], (int) $_POST['decimals'], isset($_POST['thousands']), (bool) $_POST['position'], (bool) $_POST['spacing']);
             $mask = $wizard->format();
             $example = (string) NumberFormat::toFormattedString((float) $_POST['number'], $mask);
             $helper->log('<hr /><b>Code:</b><br />');
diff --git a/samples/Wizards/NumberFormat/Number.php b/samples/Wizards/NumberFormat/Number.php
index ab2b2b3f3..274f7904a 100644
--- a/samples/Wizards/NumberFormat/Number.php
+++ b/samples/Wizards/NumberFormat/Number.php
@@ -49,11 +49,11 @@ if ($helper->isCli()) {
 if (isset($_POST['submit'])) {
     if (!is_numeric($_POST['number'])) {
         $helper->log('The Sample Number Value must be numeric');
-    } elseif (!is_numeric($_POST['decimals']) || str_contains($_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
+    } elseif (!is_numeric($_POST['decimals']) || str_contains((string) $_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
         $helper->log('The Decimal Places value must be positive integer');
     } else {
         try {
-            $wizard = new Wizard\Number($_POST['decimals'], isset($_POST['thousands']));
+            $wizard = new Wizard\Number((int) $_POST['decimals'], isset($_POST['thousands']));
             $mask = $wizard->format();
             $example = NumberFormat::toFormattedString((float) $_POST['number'], $mask);
             $helper->log('<hr /><b>Code:</b><br />');
diff --git a/samples/Wizards/NumberFormat/Percentage.php b/samples/Wizards/NumberFormat/Percentage.php
index c1838827b..71b5c6911 100644
--- a/samples/Wizards/NumberFormat/Percentage.php
+++ b/samples/Wizards/NumberFormat/Percentage.php
@@ -43,11 +43,11 @@ if ($helper->isCli()) {
 if (isset($_POST['submit'])) {
     if (!is_numeric($_POST['number'])) {
         $helper->log('The Sample Number Value must be numeric');
-    } elseif (!is_numeric($_POST['decimals']) || str_contains($_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
+    } elseif (!is_numeric($_POST['decimals']) || str_contains((string) $_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
         $helper->log('The Decimal Places value must be positive integer');
     } else {
         try {
-            $wizard = new Wizard\Percentage($_POST['decimals']);
+            $wizard = new Wizard\Percentage((int) $_POST['decimals']);
             $mask = $wizard->format();
             $example = (string) NumberFormat::toFormattedString((float) $_POST['number'], $mask);
             $helper->log('<hr /><b>Code:</b><br />');
diff --git a/samples/Wizards/NumberFormat/Scientific.php b/samples/Wizards/NumberFormat/Scientific.php
index 40d390a5e..61e635d78 100644
--- a/samples/Wizards/NumberFormat/Scientific.php
+++ b/samples/Wizards/NumberFormat/Scientific.php
@@ -43,11 +43,11 @@ if ($helper->isCli()) {
 if (isset($_POST['submit'])) {
     if (!is_numeric($_POST['number'])) {
         $helper->log('The Sample Number Value must be numeric');
-    } elseif (!is_numeric($_POST['decimals']) || str_contains($_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
+    } elseif (!is_numeric($_POST['decimals']) || str_contains((string) $_POST['decimals'], '.') || (int) $_POST['decimals'] < 0) {
         $helper->log('The Decimal Places value must be positive integer');
     } else {
         try {
-            $wizard = new Wizard\Scientific($_POST['decimals']);
+            $wizard = new Wizard\Scientific((int) $_POST['decimals']);
             $mask = $wizard->format();
             $example = (string) NumberFormat::toFormattedString((float) $_POST['number'], $mask);
             $helper->log('<hr /><b>Code:</b><br />');
diff --git a/samples/templates/sampleSpreadsheet.php b/samples/templates/sampleSpreadsheet.php
index 92e88262d..998f21105 100644
--- a/samples/templates/sampleSpreadsheet.php
+++ b/samples/templates/sampleSpreadsheet.php
@@ -74,19 +74,19 @@ $helper->log('Add comments');
 
 $spreadsheet->getActiveSheet()->getComment('E11')->setAuthor('PhpSpreadsheet');
 $commentRichText = $spreadsheet->getActiveSheet()->getComment('E11')->getText()->createTextRun('PhpSpreadsheet:');
-$commentRichText->getFont()->setBold(true);
+$commentRichText->getFontOrThrow()->setBold(true);
 $spreadsheet->getActiveSheet()->getComment('E11')->getText()->createTextRun("\r\n");
 $spreadsheet->getActiveSheet()->getComment('E11')->getText()->createTextRun('Total amount on the current invoice, excluding VAT.');
 
 $spreadsheet->getActiveSheet()->getComment('E12')->setAuthor('PhpSpreadsheet');
 $commentRichText = $spreadsheet->getActiveSheet()->getComment('E12')->getText()->createTextRun('PhpSpreadsheet:');
-$commentRichText->getFont()->setBold(true);
+$commentRichText->getFontOrThrow()->setBold(true);
 $spreadsheet->getActiveSheet()->getComment('E12')->getText()->createTextRun("\r\n");
 $spreadsheet->getActiveSheet()->getComment('E12')->getText()->createTextRun('Total amount of VAT on the current invoice.');
 
 $spreadsheet->getActiveSheet()->getComment('E13')->setAuthor('PhpSpreadsheet');
 $commentRichText = $spreadsheet->getActiveSheet()->getComment('E13')->getText()->createTextRun('PhpSpreadsheet:');
-$commentRichText->getFont()->setBold(true);
+$commentRichText->getFontOrThrow()->setBold(true);
 $spreadsheet->getActiveSheet()->getComment('E13')->getText()->createTextRun("\r\n");
 $spreadsheet->getActiveSheet()->getComment('E13')->getText()->createTextRun('Total amount on the current invoice, including VAT.');
 $spreadsheet->getActiveSheet()->getComment('E13')->setWidth('100pt');
@@ -100,9 +100,9 @@ $richText = new RichText();
 $richText->createText('This invoice is ');
 
 $payable = $richText->createTextRun('payable within thirty days after the end of the month');
-$payable->getFont()->setBold(true);
-$payable->getFont()->setItalic(true);
-$payable->getFont()->setColor(new Color(Color::COLOR_DARKGREEN));
+$payable->getFontOrThrow()->setBold(true);
+$payable->getFontOrThrow()->setItalic(true);
+$payable->getFontOrThrow()->setColor(new Color(Color::COLOR_DARKGREEN));
 
 $richText->createText(', unless specified otherwise on the invoice.');
 
diff --git a/samples/templates/sampleSpreadsheet2.php b/samples/templates/sampleSpreadsheet2.php
index 5a7beda70..76b5e0454 100644
--- a/samples/templates/sampleSpreadsheet2.php
+++ b/samples/templates/sampleSpreadsheet2.php
@@ -74,19 +74,19 @@ $helper->log('Add comments');
 
 $spreadsheet->getActiveSheet()->getComment('E11')->setAuthor('PhpSpreadsheet');
 $commentRichText = $spreadsheet->getActiveSheet()->getComment('E11')->getText()->createTextRun('PhpSpreadsheet:');
-$commentRichText->getFont()->setBold(true);
+$commentRichText->getFontOrThrow()->setBold(true);
 $spreadsheet->getActiveSheet()->getComment('E11')->getText()->createTextRun("\r\n");
 $spreadsheet->getActiveSheet()->getComment('E11')->getText()->createTextRun('Total amount on the current invoice, excluding VAT.');
 
 $spreadsheet->getActiveSheet()->getComment('E12')->setAuthor('PhpSpreadsheet');
 $commentRichText = $spreadsheet->getActiveSheet()->getComment('E12')->getText()->createTextRun('PhpSpreadsheet:');
-$commentRichText->getFont()->setBold(true);
+$commentRichText->getFontOrThrow()->setBold(true);
 $spreadsheet->getActiveSheet()->getComment('E12')->getText()->createTextRun("\r\n");
 $spreadsheet->getActiveSheet()->getComment('E12')->getText()->createTextRun('Total amount of VAT on the current invoice.');
 
 $spreadsheet->getActiveSheet()->getComment('E13')->setAuthor('PhpSpreadsheet');
 $commentRichText = $spreadsheet->getActiveSheet()->getComment('E13')->getText()->createTextRun('PhpSpreadsheet:');
-$commentRichText->getFont()->setBold(true);
+$commentRichText->getFontOrThrow()->setBold(true);
 $spreadsheet->getActiveSheet()->getComment('E13')->getText()->createTextRun("\r\n");
 $spreadsheet->getActiveSheet()->getComment('E13')->getText()->createTextRun('Total amount on the current invoice, including VAT.');
 $spreadsheet->getActiveSheet()->getComment('E13')->setWidth('100pt');
@@ -100,9 +100,9 @@ $richText = new RichText();
 $richText->createText('This invoice is ');
 
 $payable = $richText->createTextRun('payable within thirty days after the end of the month');
-$payable->getFont()->setBold(true);
-$payable->getFont()->setItalic(true);
-$payable->getFont()->setColor(new Color(Color::COLOR_DARKGREEN));
+$payable->getFontOrThrow()->setBold(true);
+$payable->getFontOrThrow()->setItalic(true);
+$payable->getFontOrThrow()->setColor(new Color(Color::COLOR_DARKGREEN));
 
 $richText->createText(', unless specified otherwise on the invoice.');
 
diff --git a/src/PhpSpreadsheet/Cell/DataValidation.php b/src/PhpSpreadsheet/Cell/DataValidation.php
index 7f1b363c5..22b285b30 100644
--- a/src/PhpSpreadsheet/Cell/DataValidation.php
+++ b/src/PhpSpreadsheet/Cell/DataValidation.php
@@ -140,13 +140,13 @@ class DataValidation
     /**
      * Set Formula 1.
      *
-     * @param string $formula
+     * @param float|int|string $formula usually string, but can be number (test for equal)
      *
      * @return $this
      */
     public function setFormula1($formula): static
     {
-        $this->formula1 = $formula;
+        $this->formula1 = (string) $formula;
 
         return $this;
     }
@@ -164,13 +164,13 @@ class DataValidation
     /**
      * Set Formula 2.
      *
-     * @param string $formula
+     * @param float|int|string $formula usually string, but can be number (test for equal)
      *
      * @return $this
      */
     public function setFormula2($formula): static
     {
-        $this->formula2 = $formula;
+        $this->formula2 = (string) $formula;
 
         return $this;
     }
diff --git a/src/PhpSpreadsheet/Chart/Axis.php b/src/PhpSpreadsheet/Chart/Axis.php
index 7de219184..3f9249ced 100644
--- a/src/PhpSpreadsheet/Chart/Axis.php
+++ b/src/PhpSpreadsheet/Chart/Axis.php
@@ -124,10 +124,10 @@ class Axis extends Properties
         return $this->axisType === self::AXIS_TYPE_DATE || (bool) $this->axisNumber['numeric'];
     }
 
-    public function setAxisOption(string $key, ?string $value): void
+    public function setAxisOption(string $key, null|float|int|string $value): void
     {
         if ($value !== null && $value !== '') {
-            $this->axisOptions[$key] = $value;
+            $this->axisOptions[$key] = (string) $value;
         }
     }
 
@@ -141,11 +141,11 @@ class Axis extends Properties
         ?string $axisOrientation = null,
         ?string $majorTmt = null,
         ?string $minorTmt = null,
-        ?string $minimum = null,
-        ?string $maximum = null,
-        ?string $majorUnit = null,
-        ?string $minorUnit = null,
-        ?string $textRotation = null,
+        null|float|int|string $minimum = null,
+        null|float|int|string $maximum = null,
+        null|float|int|string $majorUnit = null,
+        null|float|int|string $minorUnit = null,
+        null|float|int|string $textRotation = null,
         ?string $hidden = null,
         ?string $baseTimeUnit = null,
         ?string $majorTimeUnit = null,
diff --git a/src/PhpSpreadsheet/Chart/Chart.php b/src/PhpSpreadsheet/Chart/Chart.php
index b86b19cdd..2b8de5d51 100644
--- a/src/PhpSpreadsheet/Chart/Chart.php
+++ b/src/PhpSpreadsheet/Chart/Chart.php
@@ -285,6 +285,16 @@ class Chart
         return $this->plotArea;
     }
 
+    public function getPlotAreaOrThrow(): PlotArea
+    {
+        $plotArea = $this->getPlotArea();
+        if ($plotArea !== null) {
+            return $plotArea;
+        }
+
+        throw new Exception('Chart has no PlotArea');
+    }
+
     /**
      * Set Plot Area.
      */
diff --git a/src/PhpSpreadsheet/Chart/DataSeries.php b/src/PhpSpreadsheet/Chart/DataSeries.php
index 8bceae071..647579345 100644
--- a/src/PhpSpreadsheet/Chart/DataSeries.php
+++ b/src/PhpSpreadsheet/Chart/DataSeries.php
@@ -124,7 +124,7 @@ class DataSeries
      * @param DataSeriesValues[] $plotCategory
      * @param DataSeriesValues[] $plotValues
      * @param null|string $plotDirection
-     * @param bool $smoothLine
+     * @param null|bool $smoothLine null treated as false
      * @param null|string $plotStyle
      */
     public function __construct($plotType = null, $plotGrouping = null, array $plotOrder = [], array $plotLabel = [], array $plotCategory = [], array $plotValues = [], $plotDirection = null, $smoothLine = false, $plotStyle = null)
@@ -144,7 +144,7 @@ class DataSeries
         }
         $this->plotCategory = $plotCategory;
 
-        $this->smoothLine = $smoothLine;
+        $this->smoothLine = (bool) $smoothLine;
         $this->plotStyle = $plotStyle;
 
         if ($plotDirection === null) {
diff --git a/src/PhpSpreadsheet/Chart/DataSeriesValues.php b/src/PhpSpreadsheet/Chart/DataSeriesValues.php
index a3f5ca0cf..72bbf8103 100644
--- a/src/PhpSpreadsheet/Chart/DataSeriesValues.php
+++ b/src/PhpSpreadsheet/Chart/DataSeriesValues.php
@@ -98,7 +98,7 @@ class DataSeriesValues extends Properties
      * @param mixed $dataValues
      * @param null|mixed $marker
      * @param null|ChartColor|ChartColor[]|string|string[] $fillColor
-     * @param string $pointSize
+     * @param int|string $pointSize point size
      */
     public function __construct($dataType = self::DATASERIES_TYPE_NUMBER, $dataSource = null, $formatCode = null, $pointCount = 0, $dataValues = [], $marker = null, $fillColor = null, $pointSize = '3')
     {
diff --git a/src/PhpSpreadsheet/Chart/Properties.php b/src/PhpSpreadsheet/Chart/Properties.php
index 849f56194..740702d12 100644
--- a/src/PhpSpreadsheet/Chart/Properties.php
+++ b/src/PhpSpreadsheet/Chart/Properties.php
@@ -795,9 +795,9 @@ abstract class Properties
      * @param string $capType
      * @param string $joinType
      * @param string $headArrowType
-     * @param string $headArrowSize
+     * @param null|int|string $headArrowSize index into ARROW_SIZES array
      * @param string $endArrowType
-     * @param string $endArrowSize
+     * @param null|int|string $endArrowSize index into ARROW_SIZES array
      * @param string $headArrowWidth
      * @param string $headArrowLength
      * @param string $endArrowWidth
@@ -824,7 +824,7 @@ abstract class Properties
         if ($headArrowType !== '') {
             $this->lineStyleProperties['arrow']['head']['type'] = $headArrowType;
         }
-        if (array_key_exists($headArrowSize, self::ARROW_SIZES)) {
+        if (isset(self::ARROW_SIZES[$headArrowSize])) {
             $this->lineStyleProperties['arrow']['head']['size'] = $headArrowSize;
             $this->lineStyleProperties['arrow']['head']['w'] = self::ARROW_SIZES[$headArrowSize]['w'];
             $this->lineStyleProperties['arrow']['head']['len'] = self::ARROW_SIZES[$headArrowSize]['len'];
@@ -832,7 +832,7 @@ abstract class Properties
         if ($endArrowType !== '') {
             $this->lineStyleProperties['arrow']['end']['type'] = $endArrowType;
         }
-        if (array_key_exists($endArrowSize, self::ARROW_SIZES)) {
+        if (isset(self::ARROW_SIZES[$endArrowSize])) {
             $this->lineStyleProperties['arrow']['end']['size'] = $endArrowSize;
             $this->lineStyleProperties['arrow']['end']['w'] = self::ARROW_SIZES[$endArrowSize]['w'];
             $this->lineStyleProperties['arrow']['end']['len'] = self::ARROW_SIZES[$endArrowSize]['len'];
diff --git a/src/PhpSpreadsheet/RichText/Run.php b/src/PhpSpreadsheet/RichText/Run.php
index c2b7156e6..05d90579e 100644
--- a/src/PhpSpreadsheet/RichText/Run.php
+++ b/src/PhpSpreadsheet/RichText/Run.php
@@ -2,6 +2,7 @@
 
 namespace PhpOffice\PhpSpreadsheet\RichText;
 
+use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
 use PhpOffice\PhpSpreadsheet\Style\Font;
 
 class Run extends TextElement implements ITextElement
@@ -35,6 +36,15 @@ class Run extends TextElement implements ITextElement
         return $this->font;
     }
 
+    public function getFontOrThrow(): Font
+    {
+        if ($this->font === null) {
+            throw new SpreadsheetException('unexpected null font');
+        }
+
+        return $this->font;
+    }
+
     /**
      * Set font.
      *
diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index 89c545852..35d3ff866 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -662,6 +662,16 @@ class Worksheet implements IComparable
         return false;
     }
 
+    public function getChartByNameOrThrow(string $chartName): Chart
+    {
+        $chart = $this->getChartByName($chartName);
+        if ($chart !== false) {
+            return $chart;
+        }
+
+        throw new Exception("Sheet does not have a chart named $chartName.");
+    }
+
     /**
      * Refresh column dimensions.
      *
diff --git a/tests/PhpSpreadsheetTests/Chart/ChartsByNameTest.php b/tests/PhpSpreadsheetTests/Chart/ChartsByNameTest.php
new file mode 100644
index 000000000..a3583672f
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Chart/ChartsByNameTest.php
@@ -0,0 +1,97 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Chart;
+
+use PhpOffice\PhpSpreadsheet\Chart\Chart;
+use PhpOffice\PhpSpreadsheet\Chart\DataSeries;
+use PhpOffice\PhpSpreadsheet\Chart\DataSeriesValues;
+use PhpOffice\PhpSpreadsheet\Chart\PlotArea;
+use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PHPUnit\Framework\TestCase;
+
+class ChartsByNameTest extends TestCase
+{
+    public function testChartByName(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->setTitle('Only Sheet');
+        $sheet->fromArray(
+            [
+                ['Some Title'],
+                [],
+                [null, null, 'Data'],
+                [null, 'L1', 1.3],
+                [null, 'L2', 1.3],
+                [null, 'L3', 2.3],
+                [null, 'L4', 1.6],
+                [null, 'L5', 1.5],
+                [null, 'L6', 1.4],
+                [null, 'L7', 2.2],
+                [null, 'L8', 1.8],
+                [null, 'L9', 1.1],
+                [null, 'L10', 1.8],
+                [null, 'L11', 1.6],
+                [null, 'L12', 2.7],
+                [null, 'L13', 2.2],
+                [null, 'L14', 1.3],
+            ]
+        );
+
+        $dataSeriesLabels = [
+            new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, '\'Only Sheet\'!$B$4', null, 1), // 2010
+        ];
+        // Set the X-Axis Labels
+        $xAxisTickValues = [
+            new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_STRING, '\'Only Sheet\'!$B$4:$B$17'),
+        ];
+        // Set the Data values for each data series we want to plot
+        $dataSeriesValues = [
+            new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, '\'Only Sheet\'!$C$4:$C$17'),
+        ];
+
+        // Build the dataseries
+        $series = new DataSeries(
+            DataSeries::TYPE_BARCHART, // plotType
+            DataSeries::GROUPING_STANDARD, // plotGrouping
+            range(0, count($dataSeriesValues) - 1), // plotOrder
+            $dataSeriesLabels, // plotLabel
+            $xAxisTickValues, // plotCategory
+            $dataSeriesValues, // plotValues
+        );
+
+        // Set the series in the plot area
+        $plotArea = new PlotArea(null, [$series]);
+
+        // Create the chart
+        $chart = new Chart(
+            name: 'namedchart1',
+            plotArea: $plotArea,
+        );
+
+        // Set the position where the chart should appear in the worksheet
+        $chart->setTopLeftPosition('G7');
+        $chart->setBottomRightPosition('N21');
+        // Add the chart to the worksheet
+        $sheet->addChart($chart);
+        $sheet->setSelectedCells('D1');
+        self::assertSame($chart, $sheet->getChartByName('namedchart1'));
+        self::assertSame($chart, $sheet->getChartByNameOrThrow('namedchart1'));
+        self::assertFalse($sheet->getChartByName('namedchart2'));
+
+        try {
+            $sheet->getChartByNameOrThrow('namedchart2');
+            $exceptionRaised = false;
+        } catch (SpreadsheetException $e) {
+            self::assertSame('Sheet does not have a chart named namedchart2.', $e->getMessage());
+            $exceptionRaised = true;
+        }
+
+        self::assertTrue($exceptionRaised);
+
+        $spreadsheet->disconnectWorksheets();
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Chart/PlotAreaTest.php b/tests/PhpSpreadsheetTests/Chart/PlotAreaTest.php
new file mode 100644
index 000000000..819e41cec
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Chart/PlotAreaTest.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Chart;
+
+use PhpOffice\PhpSpreadsheet\Chart\Chart;
+use PhpOffice\PhpSpreadsheet\Chart\DataSeries;
+use PhpOffice\PhpSpreadsheet\Chart\DataSeriesValues;
+use PhpOffice\PhpSpreadsheet\Chart\Exception as ChartException;
+use PhpOffice\PhpSpreadsheet\Chart\PlotArea;
+use PHPUnit\Framework\TestCase;
+
+class PlotAreaTest extends TestCase
+{
+    public function testPlotArea(): void
+    {
+        $dataSeriesValues = [
+            new DataSeriesValues(DataSeriesValues::DATASERIES_TYPE_NUMBER, null, null, 4, [1, 2, 3, 4]),
+        ];
+
+        // Build the dataseries
+        $series = new DataSeries(
+            plotType: DataSeries::TYPE_AREACHART,
+            plotGrouping: DataSeries::GROUPING_PERCENT_STACKED,
+            plotOrder: range(0, count($dataSeriesValues) - 1),
+            plotValues: $dataSeriesValues
+        );
+
+        // Set the series in the plot area
+        $plotArea = new PlotArea(null, [$series]);
+
+        // Create the chart
+        $chart = new Chart(
+            'chart1', // name
+            plotArea: $plotArea,
+        );
+        self::assertNotNull($chart->getPlotAreaOrThrow());
+    }
+
+    public function testNoPlotArea(): void
+    {
+        $chart = new Chart('chart1');
+        $this->expectException(ChartException::class);
+        $this->expectExceptionMessage('Chart has no PlotArea');
+        $chart->getPlotAreaOrThrow();
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/RichTextTest.php b/tests/PhpSpreadsheetTests/RichTextTest.php
index 3ebd099c0..513dcf7a9 100644
--- a/tests/PhpSpreadsheetTests/RichTextTest.php
+++ b/tests/PhpSpreadsheetTests/RichTextTest.php
@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace PhpOffice\PhpSpreadsheetTests;
 
+use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
 use PhpOffice\PhpSpreadsheet\RichText\TextElement;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -48,4 +49,20 @@ class RichTextTest extends TestCase
         self::assertSame([['ABC', '-3.5']], $sheet->toArray());
         $spreadsheet->disconnectWorksheets();
     }
+
+    public function testNullFont(): void
+    {
+        $richText = new RichText();
+        $textRun = $richText->createTextRun('hello');
+        self::assertNotNull($textRun->getFontOrThrow());
+        $textRun->setFont(null);
+
+        try {
+            $textRun->getFontOrThrow();
+            $foundFont = true;
+        } catch (SpreadsheetException $e) {
+            $foundFont = false;
+        }
+        self::assertFalse($foundFont, 'expected exception not received');
+    }
 }