TST: add test for converting 0-len Series #697
Description
are these supported?
In [3]: xray.DataArray.from_series(Series([]))
ValueError: dimensions () must have the same length as the number of data dimensions, ndim=1
In [5]: xray.Dataset.from_dataframe(DataFrame({'A' : []}))
ValueError: dimensions () must have the same length as the number of data dimensions, ndim=1