fix(callback): callback is not required

index.js

@@ -8,11 +8,17 @@ module.exports = function(app, paths, callback){
 
     annotationRouter(paths, function(err, route){
 
-        if(err) return callback(err);
+        if(err) return callCallback(err);
 
         app[route.method.toLowerCase()](route.url, route.action);
     },
     function(err){
-        callback(err);
+        callCallback(err);
     });
+
+    function callCallback(err){
+        if(callback != null){
+            callback(err);
+        }
+    }
 };

test/index.js

@@ -6,7 +6,7 @@ var expressRouter = require('../index.js');
 
 var mockPath = 'mock.js';
 
-describe('', function(){
+describe('register routes', function(){
 
     var app;
 

test/no-callback.js

@@ -0,0 +1,22 @@
+var should = require('should');
+var express = require('express');
+
+var expressRouter = require('../index.js');
+
+var mockPath = 'mock.js';
+
+
+describe('when no callback is given', function(){
+
+    var app;
+
+    before(function(){
+        app = express();
+    });
+
+    it('should not throw an error', function(done){
+        expressRouter(app, mockPath);
+
+        setTimeout(done, 1000);
+    })
+})