[Numpy-discussion] histogram2d error with empty inputs

I found another empty input edge case. Somewhat recently, we fixed an issue with np.histogram() and empty inputs (so long as the bins are somehow known).

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np.histogram([], bins=4) (array([0, 0, 0, 0]), array([ 0. , 0.25, 0.5 , 0.75, 1. ]))

However, histogram2d needs the same treatment.

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np.histogram([], [], bins=4) (array([ 0., 0.]), array([ 0. , 0.25, 0.5 , 0.75, 1. ]), array([ 0. , 0.25, 0.5 , 0.75, 1. ]))

The first element in the return tuple needs to be 4x4 (in this case). Thanks, Ben Root