BUG: put back default arg for step and type to be able to initialize an empty Paramreg object before setting its arguments (as done on line 237 and 238)
BUG: put back default arg for step and type to be able to initialize an empty Paramreg object before setting its arguments (as done on line 237 and 238)

Former-commit-id: 3f32135000ff4bf76170801e7f0f014a9893669f
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox