Error from pad default arguments

[mdtanker]

I was trying to pad a grid with method="linear_ramp", but received the following error:

ValueError: unsupported keyword arguments for mode 'linear_ramp': {'constant_values'}

This seems to be due to constant_values defaulting to 0 instead of None. Pad works fine when I manually set constant_values=None, as below.

pad_width = {
        "northing": 10,
        "easting": 10,
}
xrft.pad(
    grid,
    pad_width,
    mode="linear_ramp",
    constant_values=None,
)

Maybe this can be fixed with switching the default value of constant_value to None for all methods except for constant, or a warning can be raised to manually set constant to None.