Improve: Make regex more stable (pimcore#383)

* Improve: Make regex more stable

* Fix: Tests

Author: robertSt7

src/SearchIndexAdapter/DefaultSearch/DataObject/FieldDefinitionAdapter/TextKeywordAdapter.php

@@ -40,12 +40,12 @@ public function getIndexMapping(): array
         );
     }
 
-    public function normalize(mixed $value): ?string
+    public function normalize(mixed $value): mixed
     {
-        if ($value) {
-            return preg_replace("/src=['\"]data:[^;]+;base64,.+?['\"]/", '', $value);
+        if (is_string($value) && $value !== '') {
+            return preg_replace("/src=(['\"])data:[^;]+;base64,.+?\\1/", '', $value);
         }
 
-        return null;
+        return parent::normalize($value);
     }
 }