TYPO3 Core

See the answer from the other ticket below how to solve your problem:

The problem is that AbstractValidator requires a certain constant and many 3rd party validators do not implement it (and cannot be forced to implement a constant). So it is a programming error to rely on the non-existing constant in the class and assume that every derieved class will implement it.

You can reproduce the issue with the mailform and wtspamshield extension versions < 1.3.1.

closing this issue now.