[ONOS-7573][Test successful] Mark online does not notify peers device subsystem

Change-Id: Ie347241325047cb65c836c849bec6aebad758820
diff --git a/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java b/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java
index f4a7836..645b287 100644
--- a/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java
+++ b/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java
@@ -250,9 +250,9 @@
 
     // implement differently if desired
     @Override
-    public boolean markOnline(DeviceId deviceId) {
+    public DeviceEvent markOnline(DeviceId deviceId) {
         log.warn("Mark online not supported");
-        return false;
+        return null;
     }
 
     @Override