API: Series/DataFrame.mask(other) should default to lib.no_default instead of np.nan

[mroeschke]

In 1.4 (#44697), .where(other=) was changed from np.nan to lib.no_default.

Since mask is the analogous method to where, it's other argument should also default to lib.no_default

[rhshadrach]

Just to be sure

it's other argument should also default to np.nan lib.no_default

[mroeschke]

Just to be sure

it's other argument should also default to np.nan lib.no_default

Thanks for spotting my typo, edited my post above