Unexpected behavior for Axes3D.plot_surface(shade=None) #11154

According to the docs the kwarg shade has to be a bool. The current implementation also accepts None and translates it to False.

Relevant code segment.

shade = kwargs.pop('shade', cmap is None)
if shade:

I assume that the current behavior is an unintended implementation detail, and I propose to change the semantics of shade=None to "use default" in order to allow further code simplification using default kwargs (#11145).