Sonar fixes

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

Change-Id: Ib5ab56b2263623b297db56c5cac2c2ee80e12725
diff --git a/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java b/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java
index c1e2843..9c3ca0f 100644
--- a/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java
+++ b/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java
@@ -713,7 +713,7 @@
          */
         private PortDescription buildPortDescription(PortDescPropertyType ptype, OFPortOptical port,
                 OpenFlowOpticalSwitch opsw) {
-            checkArgument(port.getDesc().size() >= 1);
+            checkArgument(!port.getDesc().isEmpty());
 
             // Minimally functional fixture. This needs to be fixed as we add better support.
             PortNumber portNo = PortNumber.portNumber(port.getPortNo().getPortNumber());
@@ -790,7 +790,7 @@
             // Use the alias name if it's available
             String name = port.getName();
             List<OFCalientPortDescProp> props = port.getProperties();
-            if (props != null && props.size() > 0) {
+            if (props != null && !props.isEmpty()) {
                 OFCalientPortDescPropOptical propOptical = (OFCalientPortDescPropOptical) props.get(0);
                 if (propOptical != null) {
                     name = propOptical.getInAlias();
diff --git a/providers/openflow/flow/src/main/java/org/onosproject/provider/of/flow/impl/FlowModBuilderVer13.java b/providers/openflow/flow/src/main/java/org/onosproject/provider/of/flow/impl/FlowModBuilderVer13.java
index 44b839b..e63fa69 100644
--- a/providers/openflow/flow/src/main/java/org/onosproject/provider/of/flow/impl/FlowModBuilderVer13.java
+++ b/providers/openflow/flow/src/main/java/org/onosproject/provider/of/flow/impl/FlowModBuilderVer13.java
@@ -131,10 +131,10 @@
         if (treatment.clearedDeferred()) {
             instructions.add(factory().instructions().clearActions());
         }
-        if (immediateActions.size() > 0) {
+        if (!immediateActions.isEmpty()) {
             instructions.add(factory().instructions().applyActions(immediateActions));
         }
-        if (deferredActions.size() > 0) {
+        if (!deferredActions.isEmpty()) {
             instructions.add(factory().instructions().writeActions(deferredActions));
         }
         if (treatment.tableTransition() != null) {
@@ -172,13 +172,13 @@
         List<OFInstruction> instructions = Lists.newLinkedList();
 
 
-        if (immediateActions.size() > 0) {
+        if (!immediateActions.isEmpty()) {
             instructions.add(factory().instructions().applyActions(immediateActions));
         }
         if (treatment.clearedDeferred()) {
             instructions.add(factory().instructions().clearActions());
         }
-        if (deferredActions.size() > 0) {
+        if (!deferredActions.isEmpty()) {
             instructions.add(factory().instructions().writeActions(deferredActions));
         }
         if (treatment.tableTransition() != null) {
diff --git a/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/GroupBucketEntryBuilder.java b/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/GroupBucketEntryBuilder.java
index 1ba438d..58cf18e 100644
--- a/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/GroupBucketEntryBuilder.java
+++ b/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/GroupBucketEntryBuilder.java
@@ -119,7 +119,7 @@
         TrafficTreatment.Builder builder = DefaultTrafficTreatment.builder();
 
         // If this is a drop rule
-        if (actions.size() == 0) {
+        if (actions.isEmpty()) {
             builder.drop();
             return builder.build();
         }
diff --git a/providers/openflow/meter/src/main/java/org/onosproject/provider/of/meter/impl/MeterModBuilder.java b/providers/openflow/meter/src/main/java/org/onosproject/provider/of/meter/impl/MeterModBuilder.java
index 5d2a101..406337b 100644
--- a/providers/openflow/meter/src/main/java/org/onosproject/provider/of/meter/impl/MeterModBuilder.java
+++ b/providers/openflow/meter/src/main/java/org/onosproject/provider/of/meter/impl/MeterModBuilder.java
@@ -155,6 +155,6 @@
     private void validate() {
         checkNotNull(id, "id cannot be null");
         checkNotNull(bands, "Must have bands");
-        checkArgument(bands.size() > 0, "Must have at lease one band");
+        checkArgument(!bands.isEmpty(), "Must have at lease one band");
     }
 }