convert VO to string

Author: peter-gribanov

Form/DataTransformer/EntitiesToPropertyTransformer.php

@@ -69,7 +69,7 @@ public function transform($entities)
                 : $this->accessor->getValue($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;