[CORD-1628] DHCP relay app configuration change for multiple servers

Change-Id: I13747d8e6451658dfd9344c428b6aad11bf5af62
(cherry picked from commit 483ac6f0689220425061056e748230efe6d8a1b2)
diff --git a/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/store/DistributedDhcpRelayStore.java b/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/store/DistributedDhcpRelayStore.java
index 60e04f9..1e87ba6 100644
--- a/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/store/DistributedDhcpRelayStore.java
+++ b/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/store/DistributedDhcpRelayStore.java
@@ -81,7 +81,7 @@
 
     @Override
     public void setDelegate(StoreDelegate<DhcpRelayStoreEvent> delegate) {
-        checkNotNull("Delegate can't be null", delegate);
+        checkNotNull(delegate, "Delegate can't be null");
         this.delegate = delegate;
     }