Sonar fixes

Rule: Use isEmpty() to check whether the collection is empty or not.

Change-Id: Ib5ab56b2263623b297db56c5cac2c2ee80e12725
diff --git a/incubator/net/src/main/java/org/onosproject/incubator/net/tunnel/impl/TunnelManager.java b/incubator/net/src/main/java/org/onosproject/incubator/net/tunnel/impl/TunnelManager.java
index a9582ab..9b8a2e7 100644
--- a/incubator/net/src/main/java/org/onosproject/incubator/net/tunnel/impl/TunnelManager.java
+++ b/incubator/net/src/main/java/org/onosproject/incubator/net/tunnel/impl/TunnelManager.java
@@ -209,7 +209,7 @@
                                               Annotations... annotations) {
         Collection<Tunnel> tunnels = store.borrowTunnel(consumerId, src,
                                                            dst, annotations);
-        if (tunnels == null || tunnels.size() == 0) {
+        if (tunnels == null || tunnels.isEmpty()) {
             Tunnel tunnel = new DefaultTunnel(null, src, dst, null, null, null,
                                               null, null, annotations);
             Set<ProviderId> ids = getProviders();
@@ -228,7 +228,7 @@
         Collection<Tunnel> tunnels = store.borrowTunnel(consumerId, src,
                                                            dst, type,
                                                            annotations);
-        if (tunnels == null || tunnels.size() == 0) {
+        if (tunnels == null || tunnels.isEmpty()) {
             Tunnel tunnel = new DefaultTunnel(null, src, dst, type, null, null,
                                               null, null, annotations);
             Set<ProviderId> ids = getProviders();
diff --git a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowRuleManager.java b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowRuleManager.java
index 31c1415..f6c6e2b 100644
--- a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowRuleManager.java
+++ b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/VirtualNetworkFlowRuleManager.java
@@ -251,7 +251,7 @@
 
         @Override
         public synchronized void run() {
-            if (stages.size() > 0) {
+            if (!stages.isEmpty()) {
                 process(stages.remove(0));
             } else if (!hasFailed) {
                 fops.callback().onSuccess(fops);
diff --git a/incubator/store/src/main/java/org/onosproject/incubator/store/tunnel/impl/DistributedTunnelStore.java b/incubator/store/src/main/java/org/onosproject/incubator/store/tunnel/impl/DistributedTunnelStore.java
index 31452ac..0907643 100644
--- a/incubator/store/src/main/java/org/onosproject/incubator/store/tunnel/impl/DistributedTunnelStore.java
+++ b/incubator/store/src/main/java/org/onosproject/incubator/store/tunnel/impl/DistributedTunnelStore.java
@@ -307,7 +307,7 @@
         orderRelationship.put(appId, orderSet);
         TunnelKey key = TunnelKey.tunnelKey(src, dst);
         Set<TunnelId> idSet = srcAndDstKeyMap.get(key);
-        if (idSet == null || idSet.size() == 0) {
+        if (idSet == null || idSet.isEmpty()) {
             return Collections.emptySet();
         }
         Collection<Tunnel> tunnelSet = new HashSet<Tunnel>();
@@ -337,7 +337,7 @@
         orderRelationship.put(appId, orderSet);
         TunnelKey key = TunnelKey.tunnelKey(src, dst);
         Set<TunnelId> idSet = srcAndDstKeyMap.get(key);
-        if (idSet == null || idSet.size() == 0) {
+        if (idSet == null || idSet.isEmpty()) {
             return Collections.emptySet();
         }
         Collection<Tunnel> tunnelSet = new HashSet<Tunnel>();
@@ -364,7 +364,7 @@
         boolean isExist = orderSet.contains(order);
 
         Set<TunnelId> idSet = tunnelNameAsKeyMap.get(tunnelName);
-        if (idSet == null || idSet.size() == 0) {
+        if (idSet == null || idSet.isEmpty()) {
             return Collections.emptySet();
         }
         Collection<Tunnel> tunnelSet = new HashSet<Tunnel>();
@@ -447,7 +447,7 @@
         for (TunnelId id : tunnelIds) {
             result.add(tunnelIdAsKeyStore.get(id));
         }
-        return result.size() == 0 ? Collections.emptySet() : ImmutableSet
+        return result.isEmpty() ? Collections.emptySet() : ImmutableSet
                 .copyOf(result);
     }
 
@@ -462,7 +462,7 @@
         for (TunnelId id : tunnelIds) {
             result.add(tunnelIdAsKeyStore.get(id));
         }
-        return result.size() == 0 ? Collections.emptySet() : ImmutableSet
+        return result.isEmpty() ? Collections.emptySet() : ImmutableSet
                 .copyOf(result);
     }