BatMap.max_binding BatMap.empty raises Invalid_argument instead of Not_found

[bnguyenvanyen]

Whereas min_binding, pop_min_binding, pop_max_binding and (all ?) others raise Not_found.
It would make more sense if it was Not_found also (but it somewhat breaks backward compatibility).

Thank you for batteries

[UnixJunkie]

This is inconsistent with the stdlib, so I think it should be fixed.

[fccm]

While doing the PR I also noticed that the Stdlib also provide exceptionless Map.min_binding_opt and Map.max_binding_opt that return an option.
Should we also add these?

[UnixJunkie]

please open a separate issue.
Note that the priority should be to do the release; such things could go into the next minor release.