Ods Reader No Datatype for Null Value

Issue #4435 was initially described incorrectly. While investigating the original description, I came upon this problem. Ods Reader is trying to set some cells to null without supplying a valid DataType to setValueExplicit, causing that method to throw an exception. Reader is changed to no longer call that method when value is null and DataType is null-string.

src/PhpSpreadsheet/Reader/Ods.php

@@ -617,7 +617,7 @@ class Ods extends BaseReader
                                                     if ($cellDataType === 'array') {
                                                         $cell->setFormulaAttributes(['t' => 'array', 'ref' => $cellDataRef]);
                                                     }
-                                                } else {
+                                                } elseif ($type !== '' || $dataValue !== null) {
                                                     $cell->setValueExplicit($dataValue, $type);
                                                 }
 

tests/PhpSpreadsheetTests/Reader/Ods/Issue4435Test.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
+
+use PhpOffice\PhpSpreadsheet\Reader\Ods as OdsReader;
+use PHPUnit\Framework\TestCase;
+
+class Issue4435Test extends TestCase
+{
+    private string $file = 'tests/data/Reader/Ods/issue.4435b.ods';
+
+    public function testNoHeaderFooterStyle(): void
+    {
+        // had been throwing exception when cell didn't have value-type
+        $zipFile = 'zip://' . $this->file . '#content.xml';
+        $contents = (string) file_get_contents($zipFile);
+        self::assertStringContainsString(
+            '<table:table-cell table:style-name="ce1">' . "\n"
+            . '<text:p/>' . "\n"
+            . '</table:table-cell>',
+            $contents
+        );
+        $reader = new OdsReader();
+        $spreadsheet = $reader->load($this->file);
+        $sheet = $spreadsheet->getActiveSheet();
+        self::assertNull($sheet->getCell('B1')->getValue());
+        $spreadsheet->disconnectWorksheets();
+    }
+}