Translator accept null

Currently when a module tries to translate something with null, following error comes up (ErrorException is custom)
2014-09-16T11:57:12+02:00 WARN (4): exception 'ErrorException' with message 'Illegal offset type' in vendor\zendframework\zendframework\library\Zend\I18n\Translator\Translator.php:441

Should probably simply fail with non-string `$message`. I wouldn't make `null` a silent failure here.