Duplicate Null Check not required

Change-Id: I31e3702b1456b8c5b50bf8e139833bd5f818df6d

@@ -144,7 +144,6 @@ public class SubnetManager implements SubnetService {
     @Override
     public boolean updateSubnets(Iterable<Subnet> subnets) {
         checkNotNull(subnets, SUBNET_NOT_NULL);
-        if (subnets != null) {
         for (Subnet subnet : subnets) {
             if (!subnetStore.containsKey(subnet.id())) {
                 log.debug("The subnet is not exist whose identifier is {}",
@@ -160,14 +159,12 @@ public class SubnetManager implements SubnetService {
                 return false;
             }
         }
-        }
         return true;
     }
 
     @Override
     public boolean removeSubnets(Iterable<SubnetId> subnetIds) {
         checkNotNull(subnetIds, SUBNET_ID_NULL);
-        if (subnetIds != null) {
         for (SubnetId subnetId : subnetIds) {
              subnetStore.remove(subnetId);
             if (subnetStore.containsKey(subnetId)) {
@@ -176,7 +173,6 @@ public class SubnetManager implements SubnetService {
                 return false;
             }
         }
-        }
         return true;
     }