Remove traceback info.

edx/analytics/tasks/export/data_obfuscation.py

@@ -191,9 +191,12 @@ class ObfuscateCoursewareStudentModule(ObfuscateSqlDumpTask):
         # but merely transform double backslashes.
         state_str = row[4].replace('\\\\', '\\')
         try:
-            state_dict = cjson.decode(state_str, all_unicode=True)
-            # Traverse the dictionary, looking for entries that need to be scrubbed.
-            updated_state_dict = self.obfuscator.obfuscate_structure(state_dict, u"state", user_info)
+            if state_str == 'NULL':
+                updated_state_dict = {}
+            else:
+                state_dict = cjson.decode(state_str, all_unicode=True)
+                # Traverse the dictionary, looking for entries that need to be scrubbed.
+                updated_state_dict = self.obfuscator.obfuscate_structure(state_dict, u"state", user_info)
         except Exception:   # pylint:  disable=broad-except
             log.exception(u"Unable to parse state as JSON for record %s: type = %s, state = %r",
                           row[0], type(state_str), state_str)