Fixing NPE on cluster restart.

Change-Id: I94e987ae544c63ccafbe8e2cd2eea662123eb019
diff --git a/core/store/dist/src/main/java/org/onosproject/store/device/impl/GossipDeviceStore.java b/core/store/dist/src/main/java/org/onosproject/store/device/impl/GossipDeviceStore.java
index 4e6c05d..93fe74f 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/device/impl/GossipDeviceStore.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/device/impl/GossipDeviceStore.java
@@ -616,6 +616,7 @@
                 final DeviceDescriptions descs = device.get(providerId);
                 List<PortDescription> mergedList =
                         FluentIterable.from(portDescriptions)
+                                .filter(input -> input.portNumber() != null)
                                 .transform(input ->
                                     // lookup merged port description
                                     descs.getPortDesc(input.portNumber()).value()