[#6883] Fixed tracker export using "nobody" as assigned_to for unassigned tickets

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
diff --git a/ForgeTracker/forgetracker/model/ticket.py b/ForgeTracker/forgetracker/model/ticket.py
index a7b17f8..5605c70 100644
--- a/ForgeTracker/forgetracker/model/ticket.py
+++ b/ForgeTracker/forgetracker/model/ticket.py
@@ -1014,7 +1014,7 @@
             summary=self.summary,
             description=self.description,
             reported_by=self.reported_by_username,
-            assigned_to=self.assigned_to_username,
+            assigned_to=self.assigned_to_id and self.assigned_to_username or None,
             reported_by_id=self.reported_by_id and str(self.reported_by_id) or None,
             assigned_to_id=self.assigned_to_id and str(self.assigned_to_id) or None,
             status=self.status,
diff --git a/ForgeTracker/forgetracker/tests/unit/test_ticket_model.py b/ForgeTracker/forgetracker/tests/unit/test_ticket_model.py
index ca532ba..8fc8038 100644
--- a/ForgeTracker/forgetracker/tests/unit/test_ticket_model.py
+++ b/ForgeTracker/forgetracker/tests/unit/test_ticket_model.py
@@ -288,3 +288,4 @@
         assert_in('related_artifacts', json_keys)  # from Artifact
         assert_in('votes_up', json_keys)  # VotableArtifact
         assert_in('ticket_num', json_keys)  # Ticket
+        assert ticket.__json__()['assigned_to'] is None