Sonar fixes

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

Change-Id: Ib5ab56b2263623b297db56c5cac2c2ee80e12725
diff --git a/src/main/java/org/onosproject/segmentrouting/RoutingRulePopulator.java b/src/main/java/org/onosproject/segmentrouting/RoutingRulePopulator.java
index 9e215a9..b691f80 100644
--- a/src/main/java/org/onosproject/segmentrouting/RoutingRulePopulator.java
+++ b/src/main/java/org/onosproject/segmentrouting/RoutingRulePopulator.java
@@ -559,7 +559,7 @@
         }
 
         List<Port> devPorts = srManager.deviceService.getPorts(deviceId);
-        if (devPorts == null || devPorts.size() == 0) {
+        if (devPorts == null || devPorts.isEmpty()) {
             log.warn("Device {} ports not available. Unable to add MacVlan filters",
                      deviceId);
             return null;
diff --git a/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java b/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java
index 7eb6894..2bd9932 100644
--- a/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java
+++ b/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java
@@ -357,7 +357,7 @@
                         .map(IpPrefix::getIp4Prefix)
                         .collect(Collectors.toSet());
 
-        if (subnets.size() == 0) {
+        if (subnets.isEmpty()) {
             log.info(NO_SUBNET, connectPoint);
             return null;
         } else if (subnets.size() > 1) {
diff --git a/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java b/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java
index 52606cf..b76a04c 100644
--- a/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java
+++ b/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java
@@ -655,7 +655,7 @@
                     log.warn("Neighbor {} is not in the port map yet for dev:{}",
                              neighborId, deviceId);
                     return;
-                } else if (devicePortMap.get(neighborId).size() == 0) {
+                } else if (devicePortMap.get(neighborId).isEmpty()) {
                     log.warn("There are no ports for "
                             + "the Device {} in the port map yet", neighborId);
                     return;