Don't depend on UndefinedAtCheckerException for flow control

[geb-bot]

Originally created by Marcin Erdmann.

Depending on exceptions for flow control is a bad practice and it's not efficient. Currently in several places scattered across the codebase UndefinedAtCheckerException is caught around at verification. There should be an at verification method that does nothing in absence of an at checker on the verified class and it should be used in these places.