Avoid propagating a null chassisID

Change-Id: I028008e45d1c78d149ef654047b9c1572eb05476
diff --git a/core/api/src/main/java/org/onosproject/net/device/DefaultDeviceDescription.java b/core/api/src/main/java/org/onosproject/net/device/DefaultDeviceDescription.java
index eb5f16a..d0b7b2b 100644
--- a/core/api/src/main/java/org/onosproject/net/device/DefaultDeviceDescription.java
+++ b/core/api/src/main/java/org/onosproject/net/device/DefaultDeviceDescription.java
@@ -110,6 +110,10 @@
         this.hwVersion = hwVersion;
         this.swVersion = swVersion;
         this.serialNumber = serialNumber;
+        //Avoid propagation of null chassisID and substitute it with UNKNOWN
+        if (chassis == null) {
+            chassis = new ChassisId();
+        }
         this.chassisId = chassis;
         this.defaultAvailable = defaultAvailable;
     }