isnull not detecting NaT in PeriodIndex

[unutbu]

In [158]: x = pd.to_datetime([np.nan, '2000-1-1'])

In [159]: y = x.to_period(freq='m')

In [160]: y
Out[160]: 
<class 'pandas.tseries.period.PeriodIndex'>
[NaT, 2000-01]
Length: 2, Freq: M

In [161]: pd.isnull(x)
Out[161]: array([ True, False], dtype=bool)

In [162]: pd.isnull(y)
Out[162]: array([False, False], dtype=bool)

I think pd.isnull(y) should be returning array([True, False], dtype=bool).

[jreback]

hmm, must be taking an odd path

[jreback]

https://github.com/pydata/pandas/blob/master/pandas/core/common.py#L305 (this is done in several places)

maybe make a function

is_datetimelike(arr):
     return arr.dtype in _DATETIME_TYPE or isintance(arr, ABCPeriodIndex)