segment_cellular_images should always return the same output type

[msschwartz21]

cellSAM/cellSAM/model.py

Lines 98 to 100 in 74ebceb

	if preds is None:
	print("No cells detected.")
	return None

In the case where there are no cells, segment_cellular_images returns None which is different from the standard output of a tuple of length 3. This immediately breaks any downstream processes that rely on a standard output shape. Instead of returning None, I would return a mask of zeros and similarly "empty" versions of the two other outputs.