Fix: [center denormalizer] do not throw an error if deserializing a null center

src/Bundle/ChillMainBundle/Serializer/Normalizer/CenterNormalizer.php

@@ -31,6 +31,10 @@ class CenterNormalizer implements DenormalizerInterface, NormalizerInterface
 
     public function denormalize($data, $type, $format = null, array $context = [])
     {
+        if (null === $data) {
+            return null;
+        }
+
         if (false === array_key_exists('type', $data)) {
             throw new InvalidArgumentException('missing "type" key in data');
         }