Variable type mixup for `channel_source`

[ehrenfeu]

Parameter channel_source in duplicate_transformations() is stated to be of type int in the docstring, but defaults to None (which is of type NoneType):

python-imcflibs/src/imcflibs/imagej/bdv.py

Lines 1373 to 1399 in 26f64c9

	def duplicate_transformations(
	project_path,
	transformation_type="channel",
	channel_source=None,
	tile_source=None,
	transformation_to_use="[Replace all transformations]",
	):
	"""Duplicate / propagate transformation parameters to other channels.
	Propagate the transformation parameters generated by a previously performed
	registration of a single channel to the other channels.
	Parameters
	----------
	project_path : str
	Path to the `.xml` project.
	transformation_type : str, optional
	Transformation mode, one of `channel` (to propagate from one channel to
	all others) and `tiles` (to propagate from one tile to all others).
	channel_source : int, optional
	Reference channel nummber (starting at 1), by default None.
	tile_source : int, optional
	Reference tile, by default None.
	transformation_to_use : str, optional
	One of `[Replace all transformations]` (default) and `[Add last
	transformation only]` to specify which transformations to propagate.
	"""

Looking at line 1415 in the function body, this has the potential to fail as operator "-" is not supported for "None":

python-imcflibs/src/imcflibs/imagej/bdv.py

Line 1415 in 26f64c9

source = str(channel_source - 1)

The obvious option would be to use an int-type default, e.g. channel_source=0 or channel_source=-1 depending on what makes more sense, and then adjust the conditional here to e.g. if channel_source >=0:

python-imcflibs/src/imcflibs/imagej/bdv.py

Line 1425 in 26f64c9

if channel_source: