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This doesn't work today

from xarray.groupers import SeasonResampler

ds.chunk(time=SeasonResampler(["DJF", "MAMJ", "JAS", "ON"]))

with an obscure error because TimeResampler is special-cased:

That is a good thing because SeasonResampler sets drop_incomplete=True by default.

We should

1. Raise a better error
2. Probably add another method (memo-ized) to Resampler objects that takes an input tuple of chunks and returns a tuple of chunks, so that SeasonResampler will ignore the drop_incomplete kwarg, and not silently drop data.