fix(build): if no options were passed in, do not throw an exception.

Author: hansl

lib/broccoli/angular2-app.js

@@ -30,7 +30,7 @@ Angular2App.prototype.toTree = function() {
       'angular2/bundles/upgrade.dev.js'
     ];
 
-    if (this.options.vendorNpmFiles) {
+    if (this.options && this.options.vendorNpmFiles) {
       vendorNpmFiles = vendorNpmFiles.concat(this.options.vendorNpmFiles);
     }