Uncertainty and mask not returned from combine()

[mwcraig]

From Tim-Oliver Husser @thusser on slack:

Just took me an hour to find this "feature" in combiner.py:

def _calculate_size_of_image(ccd,
                             combine_uncertainty_function):
    # If uncertainty_func is given for combine this will create an uncertainty
    # even if the originals did not have one. In that case we need to create
    # an empty placeholder.
    if ccd.uncertainty is None and combine_uncertainty_function is not None:
        ccd.uncertainty = StdDevUncertainty(np.zeros(ccd.data.shape))

Is this really, what you want? The docstring for combine_uncertainty_function in combine() says:

    combine_uncertainty_function : callable, None, optional
        If ``None`` use the default uncertainty func when using average, median or
        sum combine, otherwise use the function provided.
        Default is ``None``.

So to me it seems totally valid to not give a combine_uncertainty_function (since it should use the default of the combine method). But in that case no uncertainties are returned from combine() . The fix would be easy, just wondering whether there is a reason for this?

[mwcraig]

Turns out that the mask isn't returned either unless the first input image has a mask....