Check for empty state

Author: CodeWithDennis

src/SelectTree.php

@@ -473,7 +473,7 @@ public function getCreateOptionAction(): ?Action
 
                 $state = $component->getMultiple()
                     ? [
-                        ...$component->getState(),
+                        ...$component->getState() ?? [],
                         $createdOptionKey,
                     ]
                     : $createdOptionKey;