ERR: consistency in rolling on empty frames #15819
Description
xref https://github.com/pandas-dev/pandas/pull/15795/files#r108178445
I think we should just return an empty frame for [4]
In [4]: DataFrame().rolling('1s').sum()
ValueError: window must be an integer
In [5]: DataFrame().rolling(1).sum()
Out[5]:
Empty DataFrame
Columns: []
Index: []
though this works.
In [7]: DataFrame(index=pd.DatetimeIndex([])).rolling(1).sum()
Out[7]:
Empty DataFrame
Columns: []
Index: []
In [8]: DataFrame(index=pd.DatetimeIndex([])).rolling('1s').sum()
Out[8]:
Empty DataFrame
Columns: []
Index: []