Series.sum has inconsistent return type #9733
Description
Series.sum returns a numpy type, except when it's empty, in which case it returns a python int of value "0":
In [2]: type(pd.Series([0]).sum())
Out[2]: numpy.int64
In [3]: type(pd.Series().sum())
Out[3]: int
This poses a problem when I do 1 / myserie.sum() because I expect to obtain np.inf rather than a divison by 0 exception.
I think the return type of Series.sum() for empty series should be inferred from the Series's dtype This way, Series([], dtype='str').sum() would return an empty string, and Series([]).sum() would return np.float64(0) since an empty series' default type seems to be float64.
Tested with Pandas 0.16.0