geb.error
Exceptions 
GebException
InvalidGebConfiguration
InvalidPageContent
NoBaseUrlDefinedException
NoNewWindowException
PageChangeListenerAlreadyRegisteredException
UnableToLoadAnyDriversException
UnableToLoadException
UnableToSetElementException
UndefinedAtCheckerException
UndefinedPageContentException
UnexpectedPageException
UnknownDriverShortNameException
UnresolvablePropertyException
Errors 
GebAssertionError
RequiredPageContentNotPresent
RequiredPageValueNotPresent