Fix pd.NaT - Series (#19251)

Author: jbrockmendel

doc/source/whatsnew/v0.23.0.txt

@@ -423,10 +423,10 @@ Conversion
 - Bug in :class:`WeekOfMonth` and :class:`LastWeekOfMonth` where default keyword arguments for constructor raised ``ValueError`` (:issue:`19142`)
 - Bug in localization of a naive, datetime string in a ``Series`` constructor with a ``datetime64[ns, tz]`` dtype (:issue:`174151`)
 - :func:`Timestamp.replace` will now handle Daylight Savings transitions gracefully (:issue:`18319`)
-
-
-
+-
+-
 - Bug in ``.astype()`` to non-ns timedelta units would hold the incorrect dtype (:issue:`19176`, :issue:`19223`, :issue:`12425`)
+- Bug in subtracting :class:`Series` from ``NaT`` incorrectly returning ``NaT`` (:issue:`19158`)
 
 
 Indexing

pandas/_libs/tslibs/nattype.pyx

@@ -156,7 +156,7 @@ cdef class _NaT(datetime):
             neg_other = -other
             return self + neg_other
 
-        elif getattr(other, '_typ', None) in ['period',
+        elif getattr(other, '_typ', None) in ['period', 'series',
                                               'periodindex', 'dateoffset']:
             return NotImplemented
 

pandas/tests/scalar/test_nat.py

@@ -314,8 +314,7 @@ def test_nat_arithmetic_index():
 
 @pytest.mark.parametrize('box, assert_func', [
     (TimedeltaIndex, tm.assert_index_equal),
-    pytest.param(Series, tm.assert_series_equal,
-                 marks=pytest.mark.xfail(reason='NaT - Series returns NaT'))
+    (Series, tm.assert_series_equal)
 ])
 def test_nat_arithmetic_td64_vector(box, assert_func):
     # GH#19124