fix #130

Author: fgnass

lib/hook.js

@@ -17,10 +17,12 @@ module.exports = function (cfg, wrapper, callback) {
    * Patch the specified method to watch the file at the given argument
    * index.
    */
-  function patch(obj, method, fileArgIndex) {
+  function patch(obj, method, optionsArgIndex) {
     var orig = obj[method];
+    if (!orig) return;
     obj[method] = function () {
-      var file = arguments[fileArgIndex];
+      var opts = arguments[optionsArgIndex];
+      var file = typeof opts == 'string' ? opts : opts.filename;
       if (file) callback(file);
       return orig.apply(this, arguments);
     };