Merge pull request #89 from Wizek/master

Call back even if the collection was empty to begin with.

lib/adapters/mongoose.js

@@ -183,6 +183,7 @@ MongooseAdapter.prototype.destroyAll = function destroyAll(model, callback) {
     this._models[model].find(function (err, data) {
         if (err) return callback(err);
         wait = data.length;
+        if (!data.length) return callback(null);
         data.forEach(function (obj) {
             obj.remove(done)
         });