Duplicate Null Check not required

Change-Id: I9b150ad11572cd44b540e5b1a893b3c7a8953c30

@@ -154,7 +154,6 @@ public class RouterManager implements RouterService {
     @Override
     public boolean updateRouters(Collection<Router> routers) {
         checkNotNull(routers, ROUTER_NOT_NULL);
-        if (routers != null) {
         for (Router router : routers) {
             if (!routerStore.containsKey(router.id())) {
                 log.debug("The routers is not exist whose identifier is {}",
@@ -170,14 +169,12 @@ public class RouterManager implements RouterService {
                 return false;
             }
         }
-        }
         return true;
     }
 
     @Override
     public boolean removeRouters(Collection<RouterId> routerIds) {
         checkNotNull(routerIds, ROUTER_ID_NULL);
-        if (routerIds != null) {
         for (RouterId routerId : routerIds) {
             if (!routerStore.containsKey(routerId)) {
                 log.debug("The router is not exist whose identifier is {}",
@@ -193,7 +190,6 @@ public class RouterManager implements RouterService {
                 return false;
             }
         }
-        }
         return true;
     }