Fix closure compiler in network_list.js.

chrome/browser/resources/options/chromeos/network_list.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * This partially describes the network list entries passed to
  * refreshNetworkData. The contents of those lists actually match
  * CrOnc.NetworkConfigType with the addition of the policyManaged property.
  * TODO(stevenjb): Use networkingPrivate.getNetworks.
  * @typedef {{
@@ skipping 1282 matching lines @@
    *     list of entries.
    * @private
    */
   function createAddVPNConnectionEntries_() {
     var entries = [];
     var providers = options.VPNProviders.getProviders();
     for (var i = 0; i < providers.length; ++i) {
       entries.push({
         label: loadTimeData.getStringF('addConnectionVPNTemplate',
                                        providers[i].name),
-        command: createVPNConnectionCallback_(providers[i].extensionID),
+        command: createVPNConnectionCallback_(
+            providers[i].extensionID || undefined),
         data: {}
       });
     }
     return entries;
   }
 
   /**
    * Whether the Network list is disabled. Only used for display purpose.
    */
   cr.defineProperty(NetworkList, 'disabled', cr.PropertyKind.BOOL_ATTR);
 
   // Export
   return {
     NetworkList: NetworkList
   };
 });