Remove unnecessary null coalescing

If the return value is `null`, it will return `null` anyway. If the method doesn't exist, it will throw an `Error` because of the undefined method.

src/Meta/Reflection.php

@@ -73,6 +73,6 @@ class Reflection
             return $properties[0]->value;
         }
 
-        return $metaProperty::defaultValue() ?? null;
+        return $metaProperty::defaultValue();
     }
 }