diff --git a/src/main/java/org/onosproject/t3/api/StaticPacketTrace.java b/src/main/java/org/onosproject/t3/api/StaticPacketTrace.java
index 149cba7..084b25e 100644
--- a/src/main/java/org/onosproject/t3/api/StaticPacketTrace.java
+++ b/src/main/java/org/onosproject/t3/api/StaticPacketTrace.java
@@ -137,7 +137,7 @@
      * @return the list of Groups for this device.
      */
     public List<GroupsInDevice> getGroupOuputs(DeviceId deviceId) {
-        return outputsForDevice.get(deviceId);
+        return outputsForDevice.get(deviceId) == null ? null : ImmutableList.copyOf(outputsForDevice.get(deviceId));
     }
 
     /**
@@ -198,6 +198,7 @@
 
     /**
      * Return if this trace is successful.
+     *
      * @return true if successful
      */
     public boolean isSuccess() {
@@ -206,6 +207,7 @@
 
     /**
      * Sets if this trace is successful.
+     *
      * @param success true if trace is successful.
      */
     public void setSuccess(boolean success) {