Calling shift(n != 0) on an empty DatetimeIndex raises an IndexError

[chazmo03]

Calling shift(0) on an empty DatetimeIndex seems to return an empty index, but calling shift(n) with a non-zero n raises an IndexError. I would expect this to return an empty index.

# this works
pd.date_range(start='20161021', end='20161021', freq='BM').shift(0)

# this raises
pd.date_range(start='20161021', end='20161021', freq='BM').shift(1)
# IndexError: index 0 is out of bounds for axis 0 with size 0

pd.__version__
# u'0.18.1'

[chris-b1]

This feels like odd behavior to be relying on, but would be consistent with Series

In [20]: s = pd.Series([])

In [21]: s.shift(0)
Out[21]: Series([], dtype: float64)

In [22]: s.shift(-1)
Out[22]: Series([], dtype: float64)

[chris-b1]

xref #13026 - seems to have been a little discussion about this