cs: Switch to a stricter way of coding - this might break in a lot of places.

src/Bundle/ChillPersonBundle/Serializer/Normalizer/MembersEditorNormalizer.php

@@ -152,7 +152,7 @@ class MembersEditorNormalizer implements DenormalizerAwareInterface, Denormalize
 
     private function performChecks($data): void
     {
-        if (null == $data['concerned'] ?? null
+        if (null === $data['concerned'] ?? null
             && false === ·\is_array('concerned')) {
             throw new Exception\UnexpectedValueException("The schema does not have any key 'concerned'");
         }