'Safely get the Validator corresponding to the given key.
This function should be overridden by subclasses
Args:
key: The attribute or item to get a validator for.
Returns:
Validator associated with key or attribute.
Raises:
ValidationError: if the requested key is illegal.'

@classmethod
def GetValidator(self, key):

    raise NotImplementedError('Subclasses    of    ValidatedBase    must    override    GetValidator.')
