In edxTrackLogJSONParser.py:findResourceDisplayName(), ensured that if display name not found, the return is an empty string, not None.
In edxTrackLogJSONParser.py:findResourceDisplayName(), ensured that if display name not found, the return is an empty string, not None.

paepcke/json_to_relation,paepcke/json_to_relation,paepcke/json_to_relation,paepcke/json_to_relation