minor fix

SAS/TMSS/backend/src/tmss/tmssapp/models/scheduling.py

@@ -241,7 +241,7 @@ class Subtask(RefreshFromDbInvalidatesCachedPropertiesMixin, ProjectPropertyMixi
             from lofar.sas.tmss.tmss.tmssapp.conversions import get_lofar2_stations
             lofar2_stations = get_lofar2_stations()
             used_stations = self.specifications_doc.get('stations', {}).get('station_list', {})
-            return all(station in lofar2_stations for station in used_stations)
+            return len(used_stations)>0 and all(station in lofar2_stations for station in used_stations)
         return False
 
     @cached_property
@@ -251,7 +251,7 @@ class Subtask(RefreshFromDbInvalidatesCachedPropertiesMixin, ProjectPropertyMixi
             from lofar.sas.tmss.tmss.tmssapp.conversions import get_lofar2_stations
             lofar2_stations = get_lofar2_stations()
             used_stations = self.specifications_doc.get('stations', {}).get('station_list', {})
-            return any(station in lofar2_stations for station in used_stations)
+            return len(used_stations)>0 and any(station in lofar2_stations for station in used_stations)
         return False
 
     @property