Minor comments

Author: Carlos Souza

pandas/core/generic.py

@@ -3972,7 +3972,7 @@ def asof(self, where, subset=None):
             where = Index(where) if is_list else Index([where])
 
         nulls = self.isnull() if is_series else self[subset].isnull().any(1)
-        if nulls.all():
+        if nulls.values.all():
             if is_series:
                 return pd.Series(np.nan, index=where)
             else:

pandas/tests/frame/test_asof.py

@@ -82,7 +82,8 @@ def test_missing(self):
         tm.assert_frame_equal(result, expected)
 
     def test_all_nans(self):
-        # series is all nans
+        # GH 15713
+        # DataFrame is all nans
         result = DataFrame([np.nan]).asof([0])
         expected = DataFrame([np.nan])
         tm.assert_frame_equal(result, expected)

pandas/tests/series/test_asof.py

@@ -150,6 +150,7 @@ def test_errors(self):
             s.asof(s.index[0], subset='foo')
 
     def test_all_nans(self):
+        # GH 15713
         # series is all nans
         result = Series([np.nan]).asof([0])
         expected = Series([np.nan])
@@ -167,4 +168,4 @@ def test_all_nans(self):
         # testing scalar input
         date = date_range('1/1/1990', periods=N * 3, freq='25s')[0]
         result = Series(np.nan, index=rng).asof(date)
-        self.assertTrue(result != result)
+        assert isnull(result)