Http 500 after adding non existing fake language

Please try to add language es_EX
following error ocurrs:
2011-09-01 09:11:49,813 [http-8083-8] ERROR errors.GrailsExceptionResolver - Executing action [execute] of controller [translate.AdminController] caused exception: java.lang.AssertionError: es_EX. Expression: (locale != null). Values: locale = null
org.codehaus.groovy.grails.web.servlet.mvc.exceptions.ControllerExecutionException: Executing action [execute] of controller [translate.AdminController] caused exception: java.lang.AssertionError: es_EX. Expression: (locale != null). Values: locale = null
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.runtime.InvokerInvocationException: java.lang.AssertionError: es_EX. Expression: (locale != null). Values: locale = null
... 1 more
Caused by: java.lang.AssertionError: es_EX. Expression: (locale != null). Values: locale = null
at translate.Language.getLocale(Language.groovy:46)
at translate.Language$getLocale$3.call(Unknown Source)
at translate.AdminController$_addLanguage_closure40.doCall(translate.AdminController:365)
at $Proxy12.doInTransaction(Unknown Source)
at translate.AdminController.addLanguage(translate.AdminController:364)
at translate.AdminController$_closure10_closure66_closure83.doCall(translate.AdminController:94)
at translate.AdminController$_closure10_closure66_closure83.doCall(translate.AdminController)
at translate.AdminController$_closure9.doCall(translate.AdminController:66)
at translate.AdminController.invokeMethod(translate.AdminController)
at translate.AdminController$_closure10_closure66.doCall(translate.AdminController:94)
at translate.AdminController$_closure10_closure66.call(translate.AdminController)
at translate.AjaxRequestProcessor$_closure2.doCall(AjaxRequestProcessor.groovy:47)
at translate.AdminController$_closure10.doCall(translate.AdminController:71)
at translate.AdminController$_closure10.doCall(translate.AdminController)
... 1 more