Refactor: Extract method to check if resource path is root

Change-Id: I87c23449c929bd169daa5fe788e340266392ddbe

@@ -93,7 +93,7 @@ public final class ResourcePath {
      * If there is no parent, empty instance will be returned.
      */
     public Optional<ResourcePath> parent() {
-        if (resources.size() > 0) {
+        if (!isRoot()) {
             return Optional.of(new ResourcePath(resources.subList(0, resources.size() - 1)));
         }
 
@@ -101,6 +101,15 @@ public final class ResourcePath {
     }
 
     /**
+     * Returns true if the path represents root.
+     *
+     * @return true if the path represents root, false otherwise.
+     */
+    public boolean isRoot() {
+        return resources.size() == 0;
+    }
+
+    /**
      * Returns the last component of this instance.
      *
      * @return the last component of this instance.

@@ -333,7 +333,7 @@ public class ConsistentResourceStore implements ResourceStore {
      */
     private boolean isRegistered(TransactionalMap<ResourcePath, List<ResourcePath>> map, ResourcePath resource) {
         // root is always regarded to be registered
-        if (!resource.parent().isPresent()) {
+        if (resource.isRoot()) {
             return true;
         }