This fixes an NPE turned up by STC testing [ONOS-7657]

Change-Id: Ic47d7a022908da2f97a8dd4c86916ae4a8d86e9c
diff --git a/apps/route-service/app/src/main/java/org/onosproject/routeservice/impl/RouteManager.java b/apps/route-service/app/src/main/java/org/onosproject/routeservice/impl/RouteManager.java
index a0ea6f5..c0d5955 100644
--- a/apps/route-service/app/src/main/java/org/onosproject/routeservice/impl/RouteManager.java
+++ b/apps/route-service/app/src/main/java/org/onosproject/routeservice/impl/RouteManager.java
@@ -270,6 +270,10 @@
     }
 
     private void resolve(RouteSet routes) {
+        if (routes.routes() == null) {
+            // The routes were removed before we got to them, nothing to do
+            return;
+        }
         Set<ResolvedRoute> resolvedRoutes = routes.routes().stream()
                 .map(this::resolve)
                 .filter(Objects::nonNull)