PHP8.1 Deprecation Passing Null to String Function (#2137)

For each of the files in this PR, one or more statements can pass a null to string functions like strlower. This is deprecated in PHP8.1, and, when deprecated messages are enabled, causes many tests to error out. In every case, use coercion to pass null string rather than null.

src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php

@@ -27,7 +27,7 @@ abstract class DatabaseAbstract
      */
     protected static function fieldExtract(array $database, $field): ?int
     {
-        $field = strtoupper(Functions::flattenSingleValue($field));
+        $field = strtoupper(Functions::flattenSingleValue($field ?? ''));
         if ($field === '') {
             return null;
         }

src/PhpSpreadsheet/Calculation/DateTimeExcel/DateValue.php

@@ -37,7 +37,7 @@ class DateValue
     {
         $dti = new DateTimeImmutable();
         $baseYear = SharedDateHelper::getExcelCalendar();
-        $dateValue = trim(Functions::flattenSingleValue($dateValue), '"');
+        $dateValue = trim(Functions::flattenSingleValue($dateValue ?? ''), '"');
         //    Strip any ordinals because they're allowed in Excel (English only)
         $dateValue = preg_replace('/(\d)(st|nd|rd|th)([ -\/])/Ui', '$1$3', $dateValue) ?? '';
         //    Convert separators (/ . or space) to hyphens (should also handle dot used for ordinals in some countries, e.g. Denmark, Germany)

src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeValue.php

@@ -31,7 +31,7 @@ class TimeValue
      */
     public static function fromString($timeValue)
     {
-        $timeValue = trim(Functions::flattenSingleValue($timeValue), '"');
+        $timeValue = trim(Functions::flattenSingleValue($timeValue ?? ''), '"');
         $timeValue = str_replace(['/', '.'], '-', $timeValue);
 
         $arraySplit = preg_split('/[\/:\-\s]/', $timeValue) ?: [];

src/PhpSpreadsheet/Calculation/TextData/Extract.php

@@ -26,7 +26,7 @@ class Extract
             $value = ($value) ? Calculation::getTRUE() : Calculation::getFALSE();
         }
 
-        return mb_substr($value, 0, $chars, 'UTF-8');
+        return mb_substr($value ?? '', 0, $chars, 'UTF-8');
     }
 
     /**
@@ -50,7 +50,7 @@ class Extract
             $value = ($value) ? Calculation::getTRUE() : Calculation::getFALSE();
         }
 
-        return mb_substr($value, --$start, $chars, 'UTF-8');
+        return mb_substr($value ?? '', --$start, $chars, 'UTF-8');
     }
 
     /**
@@ -72,6 +72,6 @@ class Extract
             $value = ($value) ? Calculation::getTRUE() : Calculation::getFALSE();
         }
 
-        return mb_substr($value, mb_strlen($value, 'UTF-8') - $chars, $chars, 'UTF-8');
+        return mb_substr($value ?? '', mb_strlen($value ?? '', 'UTF-8') - $chars, $chars, 'UTF-8');
     }
 }

src/PhpSpreadsheet/Calculation/TextData/Text.php

@@ -20,7 +20,7 @@ class Text
             $value = ($value) ? Calculation::getTRUE() : Calculation::getFALSE();
         }
 
-        return mb_strlen($value, 'UTF-8');
+        return mb_strlen($value ?? '', 'UTF-8');
     }
 
     /**

src/PhpSpreadsheet/Reader/Html.php

@@ -914,7 +914,7 @@ class Html extends BaseReader
      */
     public function getStyleColor($value)
     {
-        if (strpos($value, '#') === 0) {
+        if (strpos($value ?? '', '#') === 0) {
             return substr($value, 1);
         }
 

src/PhpSpreadsheet/Reader/Xml/PageSettings.php

@@ -115,7 +115,7 @@ class PageSettings
 
     private function setLayout(stdClass $printDefaults, SimpleXMLElement $pageSetupAttributes): void
     {
-        $printDefaults->orientation = (string) strtolower($pageSetupAttributes->Orientation) ?: PageSetup::ORIENTATION_PORTRAIT;
+        $printDefaults->orientation = (string) strtolower($pageSetupAttributes->Orientation ?? '') ?: PageSetup::ORIENTATION_PORTRAIT;
         $printDefaults->horizontalCentered = (bool) $pageSetupAttributes->CenterHorizontal ?: false;
         $printDefaults->verticalCentered = (bool) $pageSetupAttributes->CenterVertical ?: false;
     }

src/PhpSpreadsheet/Shared/StringHelper.php

@@ -502,7 +502,7 @@ class StringHelper
      */
     public static function strToLower($pValue)
     {
-        return mb_convert_case($pValue, MB_CASE_LOWER, 'UTF-8');
+        return mb_convert_case($pValue ?? '', MB_CASE_LOWER, 'UTF-8');
     }
 
     /**

src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php

@@ -1256,7 +1256,7 @@ class Worksheet extends WriterPart
             $objWriter,
             $this->getParentWriter()->getOffice2003Compatibility() === false,
             'v',
-            ($this->getParentWriter()->getPreCalculateFormulas() && !is_array($calculatedValue) && substr($calculatedValue, 0, 1) !== '#')
+            ($this->getParentWriter()->getPreCalculateFormulas() && !is_array($calculatedValue) && substr($calculatedValue ?? '', 0, 1) !== '#')
                 ? StringHelper::formatNumber($calculatedValue) : '0'
         );
     }

tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php

@@ -341,7 +341,7 @@ class FunctionsTest extends TestCase
                 ->disableOriginalConstructor()
                 ->getMock();
             $remoteCell->method('isFormula')
-                ->willReturn(substr($value, 0, 1) == '=');
+                ->willReturn(substr($value ?? '', 0, 1) == '=');
 
             $remoteSheet = $this->getMockBuilder(Worksheet::class)
                 ->disableOriginalConstructor()