geb.error
Exceptions 
GebException
InvalidPageContent
NoBaseUrlDefinedException
PageChangeListenerAlreadyRegisteredException
UnableToLoadAnyDriversException
UndefinedPageContentException
UnexpectedPageException
UnknownDriverShortNameException
UnresolvablePropertyException
Errors 
GebAssertionError
RequiredPageContentNotPresent
RequiredPageValueNotPresent