Fix: urgent fix for EntityToJsonTransformer

The throw on error flag imposes us to propose a valid json string for decoding

src/Bundle/ChillMainBundle/Form/Type/DataTransformer/EntityToJsonTransformer.php

@@ -43,6 +43,10 @@ class EntityToJsonTransformer implements DataTransformerInterface
 
     public function reverseTransform($value)
     {
+        if ("" === $value) {
+            return null;
+        }
+
         $denormalized = json_decode($value, true, 512, JSON_THROW_ON_ERROR);
 
         if ($this->multiple) {
@@ -56,10 +60,6 @@ class EntityToJsonTransformer implements DataTransformerInterface
             );
         }
 
-        if ('' === $value) {
-            return null;
-        }
-
         return $this->denormalizeOne($denormalized);
     }