[C++] unimplemented validator (should not) throws exception

[qzmfranklin]

I observed with the latest main that the email validator isn't implemented yet.

It throws an excpetion like this:

I can understand that this alerts developers so that they don't have the false impression that the object is valid. But it is a pain for developers who just want to validate as much as possible.

Could there a be a flag that changes the behavior to a warning or no-op? This flag could be false by default.