Use concrete type instead of interface

Change-Id: Id36816eb7711305c01b47d73048cc6a3c868405f
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
index c3d63d6..9211576 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
@@ -27,7 +27,7 @@
  * Represents an empty set of discrete resource.
  */
 final class EmptyDiscreteResources implements DiscreteResources {
-    static final DiscreteResources INSTANCE = new EmptyDiscreteResources();
+    static final EmptyDiscreteResources INSTANCE = new EmptyDiscreteResources();
 
     // for serializer
     private EmptyDiscreteResources() {}