[ONOS-4992] Modify the return signature for FlowRuleService for consistent return object

Change-Id: I06154d79ea9d875c503369dcb77d5fffcfbd4467
diff --git a/core/api/src/test/java/org/onosproject/net/flow/FlowRuleServiceAdapter.java b/core/api/src/test/java/org/onosproject/net/flow/FlowRuleServiceAdapter.java
index 4335983..297e553 100644
--- a/core/api/src/test/java/org/onosproject/net/flow/FlowRuleServiceAdapter.java
+++ b/core/api/src/test/java/org/onosproject/net/flow/FlowRuleServiceAdapter.java
@@ -55,6 +55,11 @@
     }
 
     @Override
+    public Iterable<FlowEntry> getFlowEntriesById(ApplicationId id) {
+        return null;
+    }
+
+    @Override
     public Iterable<FlowRule> getFlowRulesByGroupId(ApplicationId appId, short groupId) {
         return null;
     }