diff --git a/src/main/java/net/onrc/onos/core/packetservice/PacketModule.java b/src/main/java/net/onrc/onos/core/packetservice/PacketModule.java
index 9cf618a..4cfb9e7 100644
--- a/src/main/java/net/onrc/onos/core/packetservice/PacketModule.java
+++ b/src/main/java/net/onrc/onos/core/packetservice/PacketModule.java
@@ -132,8 +132,11 @@
     @Override
     public void broadcastPacketOutInternalEdge(Ethernet eth, SwitchPort inSwitchPort) {
 
-        Set<SwitchPort> blacklistSwitchPorts = new HashSet<SwitchPort>(configService
-                .getExternalSwitchPorts());
+        Set<SwitchPort> blacklistSwitchPorts = new HashSet<SwitchPort>();
+        Set<SwitchPort> externalSwitchPorts = configService.getExternalSwitchPorts();
+        if (externalSwitchPorts != null) {
+            blacklistSwitchPorts.addAll(externalSwitchPorts);
+        }
         blacklistSwitchPorts.add(inSwitchPort);
 
         BroadcastPacketOutNotification notification =