chore(dataframe_client): update to handle empty tags in dataframe client (#814)

Author: sebito91

CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fix nanosecond time resolution for points (#407 thx @AndreCAndersen && @clslgrnc)
 - Fix import of distutils.spawn (#805 thx @Hawk777)
 - Update repr of float values including properly handling of boolean (#488 thx @ghost)
+- Update dataframe_client to fix faulty empty tags (#770 thx @michelfripiat)
 
 ### Removed
 

influxdb/_dataframe_client.py

@@ -388,7 +388,8 @@ def _convert_dataframe_to_lines(self,
             del tag_df
         elif global_tags:
             tag_string = ''.join(
-                [",{}={}".format(k, _escape_tag(v)) if v else ''
+                [",{}={}".format(k, _escape_tag(v))
+                 if v not in [None, ''] else ""
                  for k, v in sorted(global_tags.items())]
             )
             tags = pd.Series(tag_string, index=dataframe.index)