Passing an identifier string (not in a list) silently truncates it

[ghyatzo]

Hello,

I've got bitten by this bug (not sure if it is fair to call it a bug, maybe more a footgun):

        assert len(identifier) > 0
        request["CoverageID"] = identifier[0]

The code above that checks for the coverage will silently truncate the coverage id if it is passed as a single string. i.e.

    response = wcs.getCoverage(
        identifier="some_id",
        format="image/tiff",
        subsets=[
            ("lat", bounds.south, bounds.north),
            ("lon", bounds.west, bounds.east)
        ],
        interpolation="nearest"
    )

If the desired api is using only lists, then It would make more sense to check for it directly and possibly error early explaining what happened.

Thanks for your work!