Exposed by rBeaa44afe703e.
Definition for CONSTRAINT_TYPE_NULL is not totally clear (it is set for
constraints without data, see an old comment from Ton), but for these, a
TypeInfo cannot be fetched.
Avoid processing those constraints in UI code, just do nothing instead.
Maniphest Tasks: T84367
Differential Revision: https://developer.blender.org/D9987