Fix: resolve a NPE caused by empty MAC info in interface object

Change-Id: I8c926759faf6ce7d7ef38f1139921bf4a37f57c5
(cherry picked from commit bc5787ee3d8421118c78a70ccce6e7787c462cf0)
diff --git a/apps/kubevirt-networking/app/src/main/java/org/onosproject/kubevirtnetworking/util/KubevirtNetworkingUtil.java b/apps/kubevirt-networking/app/src/main/java/org/onosproject/kubevirtnetworking/util/KubevirtNetworkingUtil.java
index 8b95507..d1ec93f 100644
--- a/apps/kubevirt-networking/app/src/main/java/org/onosproject/kubevirtnetworking/util/KubevirtNetworkingUtil.java
+++ b/apps/kubevirt-networking/app/src/main/java/org/onosproject/kubevirtnetworking/util/KubevirtNetworkingUtil.java
@@ -424,7 +424,7 @@
                         .filter(n -> (NETWORK_PREFIX + n.name()).equals(name) ||
                                      (n.name() + "-net").equals(name))
                         .findAny().orElse(null);
-                if (network != null) {
+                if (network != null && interfaceJson.get(MAC) != null) {
                     // FIXME: we do not update IP address, as learning IP address
                     // requires much more time due to the lag from VM agent
                     String mac = interfaceJson.get(MAC).asText();