diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyEvent.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyEvent.java
index 397fac5..2892e0c 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyEvent.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/TopologyEvent.java
@@ -76,7 +76,7 @@
 	    return linkEvent.toString();
 	if (deviceEvent != null)
 	    return deviceEvent.toString();
-	return null;
+	return "[Empty TopologyEvent]";
     }
 
     /**