Merge pull request #8268 from jreback/nat

TST: tests for reduction of series with nan timedelta (GH7661)

Author: jreback

doc/source/v0.15.0.txt

@@ -479,7 +479,7 @@ TimedeltaIndex/Scalar
 We introduce a new scalar type ``Timedelta``, which is a subclass of ``datetime.timedelta``, and behaves in a similar manner,
 but allows compatibility with ``np.timedelta64`` types as well as a host of custom representation, parsing, and attributes.
 This type is very similar to how ``Timestamp`` works for ``datetimes``. It is a nice-API box for the type. See the :ref:`docs <timedeltas.timedeltas>`.
-(:issue:`3009`, :issue:`4533`, :issue:`8209`, :issue:`8187`, :issue:`8190`, :issue:`7869`)
+(:issue:`3009`, :issue:`4533`, :issue:`8209`, :issue:`8187`, :issue:`8190`, :issue:`7869`, :issue:`7661`)
 
 .. warning::
 

pandas/tests/test_series.py

@@ -2371,6 +2371,10 @@ def test_quantile(self):
         q = tds.quantile(.25)
         self.assertEqual(q, pd.to_timedelta('24:00:00'))
 
+        # GH7661
+        result = Series([np.timedelta64('NaT')]).sum()
+        self.assertTrue(result is pd.NaT)
+
     def test_quantile_multi(self):
         from numpy import percentile