Handle all-empty tags

Author: tzonghao

influxdb/_dataframe_client.py

@@ -291,7 +291,10 @@ def _convert_dataframe_to_lines(self,
 
             # join tags, but leave out None values
             tags = tag_df.apply(
-                lambda r: ',' + ','.join(r.dropna()), axis=1)
+                lambda r: ','.join(r.dropna()), axis=1)
+
+            # prepend comma
+            tags = tags.apply(lambda v: ',' + v if v else '')
 
             del tag_df
         else:

influxdb/tests/dataframe_client_test.py

@@ -206,8 +206,9 @@ def test_write_points_from_dataframe_with_tag_escaped(self):
                 ['red,green', "2", 2, r'cold\fire'],  # comma, backslash
                 ['some', "2", 2, ''],                 # skip empty
                 ['some', "2", 2, None],               # skip None
+                ['', "2", 2, None],                   # all tags empty
             ],
-            index=pd.period_range(now, freq='H', periods=4),
+            index=pd.period_range(now, freq='H', periods=5),
             columns=["tag_one", "column_one", "column_two", "tag_three"]
         )
 
@@ -224,6 +225,9 @@ def test_write_points_from_dataframe_with_tag_escaped(self):
             b"foo,tag_one=some "
             b"column_one=\"2\",column_two=2i "
             b"10800000000000\n"
+            b"foo "
+            b"column_one=\"2\",column_two=2i "
+            b"14400000000000\n"
         )
 
         with requests_mock.Mocker() as m: