make Filter object immutable

Change-Id: I73063506cab0200449197245e8be85d3868d5327
diff --git a/apps/restconf/restconfmgr/src/main/java/org/onosproject/restconf/restconfmanager/RestconfManager.java b/apps/restconf/restconfmgr/src/main/java/org/onosproject/restconf/restconfmanager/RestconfManager.java
index c166050..356306d 100644
--- a/apps/restconf/restconfmgr/src/main/java/org/onosproject/restconf/restconfmanager/RestconfManager.java
+++ b/apps/restconf/restconfmgr/src/main/java/org/onosproject/restconf/restconfmanager/RestconfManager.java
@@ -109,7 +109,7 @@
             throws RestconfException {
         ResourceId rid = convertUriToRid(uri);
         // TODO: define Filter (if there is any requirement).
-        Filter filter = new Filter();
+        Filter filter = Filter.builder().build();
         DataNode dataNode;
 
         try {