chore(backport release-0.8): fix(controller): fix panic when last pro…

…motion has no freight collection (#2366)

Co-authored-by: Andy Lo-A-Foe <[email protected]>

internal/controller/promotions/promotions.go

@@ -497,7 +497,7 @@ func (r *reconciler) promote(
 		Charts:  targetFreight.Charts,
 		Origin:  targetFreight.Origin,
 	}
-	targetFreightCol := r.buildTargetFreightCollection(targetFreightRef, stage)
+	targetFreightCol := r.buildTargetFreightCollection(ctx, targetFreightRef, stage)
 
 	newStatus, nextFreight, err :=
 		r.promoMechanisms.Promote(ctx, stage, &promo, targetFreightCol.References())
@@ -544,20 +544,26 @@ func (r *reconciler) promote(
 // FreightReferences from the previous Promotion (excepting those that are no
 // longer requested), plus a FreightReference for the provided targetFreight.
 func (r *reconciler) buildTargetFreightCollection(
+	ctx context.Context,
 	targetFreight kargoapi.FreightReference,
 	stage *kargoapi.Stage,
 ) *kargoapi.FreightCollection {
+	logger := logging.LoggerFromContext(ctx)
 	freightCol := &kargoapi.FreightCollection{}
 
 	// We don't simply copy the current FreightCollection because we want to
 	// account for the possibility that some freight contained therein are no
 	// longer requested by the Stage.
-	lastPromo := stage.Status.LastPromotion
-	if lastPromo != nil {
-		for _, req := range stage.Spec.RequestedFreight {
-			if freight, ok := lastPromo.Status.FreightCollection.Freight[req.Origin.String()]; ok {
-				freightCol.UpdateOrPush(freight)
+	if len(stage.Spec.RequestedFreight) > 1 {
+		lastPromo := stage.Status.LastPromotion
+		if lastPromo.Status != nil && lastPromo.Status.FreightCollection != nil {
+			for _, req := range stage.Spec.RequestedFreight {
+				if freight, ok := lastPromo.Status.FreightCollection.Freight[req.Origin.String()]; ok {
+					freightCol.UpdateOrPush(freight)
+				}
 			}
+		} else {
+			logger.Debug("last promotion has no collection to inherit Freight from")
 		}
 	}
 	freightCol.UpdateOrPush(targetFreight)