convert VO to string

Author: peter-gribanov

Form/DataTransformer/EntityToPropertyTransformer.php

@@ -68,7 +68,7 @@ public function transform($entity)
             : $this->accessor->getValue($entity, $this->textProperty);
 
         if ($this->em->contains($entity)) {
-            $value = $this->accessor->getValue($entity, $this->primaryKey);
+            $value = (string) $this->accessor->getValue($entity, $this->primaryKey);
         } else {
             $value = $this->newTagPrefix . $text;
             $text = $text.$this->newTagText;