add better differences to check if arrival candidates exist

aman/sys/aco/Node.py

@@ -155,7 +155,7 @@ class Node:
         self.PredictedDistanceToIAF = inbound.Report.distanceToIAF
         self.PredictedCoordinate = [ inbound.CurrentPosition.latitude, inbound.CurrentPosition.longitude ]
         self.PredictionTime = referenceTime
-        self.ArrivalCandidates = {}
+        self.ArrivalCandidates = None
         self.Inbound = inbound
 
         if None == referenceTime or None == sequencingConfig:
@@ -185,6 +185,7 @@ class Node:
                 self.PredictedCoordinate = prediction
 
         setEnrouteTime = None == self.Inbound.EnrouteArrivalTime
+        self.ArrivalCandidates = {}
 
         # calculate the timings for the different arrival runways
         for identifier in sequencingConfig.ActiveArrivalRunways: