img2img Mask parm on Schema

[wscholar]

If we set the default to None it works. please add me as a contributor so I can issue a PR or update the code

'mask': {
'type': str,
'required': False,
'default': None
},

[ashleykleynhans]

You don't need to be a contributor, simply fork the repo, push your changes to your fork and submit PR.