Fixes javadoc errors

Change-Id: I85027b75520cb2087f177d282e2f5a5ec28d1b6a

@@ -113,6 +113,7 @@ public interface AsyncDocumentTree<V> extends DistributedPrimitive {
      *
      * @param path path to root of subtree to monitor for updates
      * @param listener listener to be notified
+     * @return a future that is completed when the operation completes
      */
     CompletableFuture<Void> addListener(DocumentPath path, DocumentTreeListener<V> listener);
 
@@ -120,6 +121,7 @@ public interface AsyncDocumentTree<V> extends DistributedPrimitive {
      * Unregisters a previously added listener.
      *
      * @param listener listener to unregister
+     * @return a future that is completed when the operation completes
      */
     CompletableFuture<Void> removeListener(DocumentTreeListener<V> listener);
 
@@ -127,6 +129,7 @@ public interface AsyncDocumentTree<V> extends DistributedPrimitive {
      * Registers a listener to be notified when the tree is modified.
      *
      * @param listener listener to be notified
+     * @return a future that is completed when the operation completes
      */
     default CompletableFuture<Void> addListener(DocumentTreeListener<V> listener) {
         return addListener(root(), listener);

@@ -33,8 +33,6 @@ import com.google.common.collect.Maps;
  * <p>
  * This implementation delegates execution to a backing tree implemented on top of Atomix framework.
  *
- * @See AtomixDocumentTree
- *
  * @param <V> tree node value type.
  */
 public class DefaultDistributedDocumentTree<V> implements AsyncDocumentTree<V> {