REST API for obj-nextids

Change-Id: Ibad03de0a6ffa8a478037120c84edfe6722f4d9b
(cherry picked from commit 0acb326963dda08a5eef16134eca5cba84b8e75d)
diff --git a/apps/virtual/app/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowObjectiveManager.java b/apps/virtual/app/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowObjectiveManager.java
index c4e2031..0a5a509 100644
--- a/apps/virtual/app/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowObjectiveManager.java
+++ b/apps/virtual/app/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowObjectiveManager.java
@@ -22,6 +22,8 @@
 import com.google.common.cache.RemovalNotification;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
+import com.google.common.collect.ImmutableMap;
+import org.apache.commons.lang3.tuple.Pair;
 import org.onlab.osgi.ServiceDirectory;
 import org.onlab.util.KryoNamespace;
 import org.onosproject.incubator.net.virtual.AbstractVnetService;
@@ -172,6 +174,11 @@
     }
 
     @Override
+    public Map<Pair<Integer, DeviceId>, List<String>> getNextMappingsChain() {
+        return ImmutableMap.of();
+    }
+
+    @Override
     public List<String> getNextMappings() {
         List<String> mappings = new ArrayList<>();
         Map<Integer, NextGroup> allnexts = flowObjectiveStore.getAllGroups();