Merge branch '2.7' into 2.8

* 2.7:
  [Serializer] Xml encoder throws exception for valid data
  [Form] Hardened form type tests
  fixed CS

Author: fabpot

DateFormatter/DateFormat/TimeZoneTransformer.php

@@ -96,6 +96,6 @@ public static function getEtcTimeZoneId($formattedTimeZone)
             return 'Etc/GMT'.($hours !== 0 ? $signal.$hours : '');
         }
 
-        throw new \InvalidArgumentException(sprintf("The GMT time zone '%s' does not match with the supported formats GMT[+-]HH:MM or GMT[+-]HHMM.", $formattedTimeZone));
+        throw new \InvalidArgumentException(sprintf('The GMT time zone "%s" does not match with the supported formats GMT[+-]HH:MM or GMT[+-]HHMM.', $formattedTimeZone));
     }
 }