Merge pull request #18 from tmg-digitale-medien/tmg-digitale-medien-patch-1

[TASK] Fix "undefined array key" error when creating new form

Author: mschwemer

Classes/Hook/CreateMarker.php

@@ -371,7 +371,7 @@ protected function shouldProcessField(): bool
      */
     protected function shouldRenameMarker(array $markers): bool
     {
-        return !empty($markers[$this->uid]) && !empty($this->properties['marker'])
-            && $markers[$this->uid] !== $this->properties['marker'];
+        return !empty($markers[$this->uid]) && isset($this->properties['marker']) 
+          && $markers[$this->uid] !== $this->properties['marker'];
     }
 }