Check if null for NetworkInterface.getDisplayName().

Only set display name to protocol buffer Configuration object if the
value is not null.

Author: chiaming2000

kinetic-simulator/src/main/java/com/seagate/kinetic/simulator/utility/ConfigurationUtil.java

@@ -84,7 +84,11 @@ public static Configuration getConfiguration(SimulatorEngine engine)
                 NetworkInterface ni = netInterfaces.nextElement();
 
                 itf1 = Interface.newBuilder();
-                itf1.setName(ni.getDisplayName());
+                
+                // display name could be null returned from NetworkInterface API
+                if (ni.getDisplayName() != null) {
+                    itf1.setName(ni.getDisplayName());
+                }
 
                 // set mac addr
                 byte[] mac = ni.getHardwareAddress();