BUG: fillna returns frame when inplace=True if value is a dict (pandas-dev#16156)

Author: ante012

pandas/core/generic.py

@@ -4054,7 +4054,7 @@ def fillna(self, value=None, method=None, axis=None, inplace=False,
                         continue
                     obj = result[k]
                     obj.fillna(v, limit=limit, inplace=True, downcast=downcast)
-                return result
+                return result if not inplace else None
             elif not is_list_like(value):
                 new_data = self._data.fillna(value=value, limit=limit,
                                              inplace=inplace,

pandas/tests/frame/test_missing.py

@@ -407,6 +407,9 @@ def test_fillna_inplace(self):
         df.fillna(value=0, inplace=True)
         tm.assert_frame_equal(df, expected)
 
+        expected = df.fillna(value={0:0}, inplace=True)
+        assert expected is None
+
         df[1][:4] = np.nan
         df[3][-4:] = np.nan
         expected = df.fillna(method='ffill')
@@ -415,6 +418,8 @@ def test_fillna_inplace(self):
         df.fillna(method='ffill', inplace=True)
         tm.assert_frame_equal(df, expected)
 
+
+
     def test_fillna_dict_series(self):
         df = DataFrame({'a': [nan, 1, 2, nan, nan],
                         'b': [1, 2, 3, nan, nan],

pandas/tests/series/test_missing.py

@@ -513,6 +513,9 @@ def test_fillna_inplace(self):
         expected = x.fillna(value=0)
         assert_series_equal(y, expected)
 
+        expected = x.fillna(value={'a' : 0}, inplace=True)
+        assert expected is None
+
     def test_fillna_invalid_method(self):
         try:
             self.ts.fillna(method='ffil')