Issue #2511306 by ElusiveMind, JeroenT, leolando.tan: Error: Call to a member...

Issue #2511306 by ElusiveMind, JeroenT, leolando.tan: Error: Call to a member function getElementsByTagName() in filter.module

core/lib/Drupal/Component/Utility/Html.php

@@ -292,14 +292,16 @@ public static function serialize(\DOMDocument $document) {
     $body_node = $document->getElementsByTagName('body')->item(0);
     $html = '';
 
-    foreach ($body_node->getElementsByTagName('script') as $node) {
-      static::escapeCdataElement($node);
-    }
-    foreach ($body_node->getElementsByTagName('style') as $node) {
-      static::escapeCdataElement($node, '/*', '*/');
-    }
-    foreach ($body_node->childNodes as $node) {
-      $html .= $document->saveXML($node);
+    if ($body_node !== NULL) {
+      foreach ($body_node->getElementsByTagName('script') as $node) {
+        static::escapeCdataElement($node);
+      }
+      foreach ($body_node->getElementsByTagName('style') as $node) {
+        static::escapeCdataElement($node, '/*', '*/');
+      }
+      foreach ($body_node->childNodes as $node) {
+        $html .= $document->saveXML($node);
+      }
     }
     return $html;
   }

core/tests/Drupal/Tests/Component/Utility/HtmlTest.php

@@ -312,4 +312,17 @@ public function testDecodeEntitiesAndEscape() {
     $this->assertSame('<em>répété</em>', $escaped);
   }
 
-}
+  /**
+   * Tests Html::serialize().
+   *
+   * Resolves an issue by where an empty DOMDocument object sent to serialization would
+   * cause errors in getElementsByTagName() in the serialization function.
+   *
+   * @covers ::serialize
+   */
+  public function testSerialize() {
+    $document = new \DOMDocument();
+    $result = Html::serialize($document);
+    $this->assertSame('', $result);
+  }
+}
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