Merge branch 'TMSS-1548' into 'master'

TMSS-1548: minor fix

Closes TMSS-1548

See merge request !738

SAS/TMSS/backend/src/tmss/tmssapp/adapters/reports.py

@@ -314,7 +314,7 @@ def _get_usage_mode(cycle: models.Cycle, start: datetime, stop: datetime) -> {}:
     reservations_dutch_only = reservations.filter(specifications_doc__resources__stations__contained_by=dutch_stations)
     duration_dutch_only = reservations_dutch_only.aggregate(duration=Sum(F('stop_time') - F('start_time')))['duration']
     duration = duration_dutch_only.total_seconds() - duration_sa_dutch_only.total_seconds() if duration_dutch_only and duration_sa_dutch_only else None
-    result['ILT mode']['ILT Dutch'] = duration if duration > 0 else None
+    result['ILT mode']['ILT Dutch'] = duration if duration is not None and duration > 0 else None
 
     return result