Update code

services/route_manager/src/main/java/com/futurewei/alcor/route/controller/RouterController.java

@@ -334,7 +334,7 @@ public RouteTableWebJson updateVpcRouteTable(@PathVariable String projectid, @Pa
     @DurationStatistics
     public RouteTablesWebJson getVpcRouteTables(@PathVariable String projectid, @PathVariable String vpcid) throws Exception {
 
-        List<RouteTable> routetables = null;
+        List<RouteTable> routetables = new ArrayList<>();
 
         try {
             RestPreconditionsUtil.verifyParameterNotNullorEmpty(vpcid);