diff --git a/tests/src/AuthBucket/OAuth2/Tests/NullUserProviderTest.php b/tests/src/AuthBucket/OAuth2/Tests/NullUserProviderTest.php
new file mode 100644
index 00000000..bee87cf4
--- /dev/null
+++ b/tests/src/AuthBucket/OAuth2/Tests/NullUserProviderTest.php
@@ -0,0 +1,97 @@
+<?php
+
+/**
+ * This file is part of the authbucket/oauth2 package.
+ *
+ * (c) Wong Hoi Sing Edison <hswong3i@pantarei-design.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace AuthBucket\OAuth2\Tests;
+
+use AuthBucket\OAuth2\Provider\OAuth2ServiceProvider;
+use AuthBucket\OAuth2\Tests\Entity\ModelManagerFactory;
+use Doctrine\Common\Annotations\AnnotationReader;
+use Doctrine\Common\Cache\ArrayCache;
+use Doctrine\ORM\EntityManager;
+use Doctrine\ORM\Mapping\Driver\AnnotationDriver;
+use Doctrine\ORM\Tools\Setup;
+use Silex\Application;
+use Silex\Provider\DoctrineServiceProvider;
+use Silex\Provider\FormServiceProvider;
+use Silex\Provider\SecurityServiceProvider;
+use Silex\Provider\SessionServiceProvider;
+use Silex\Provider\TwigServiceProvider;
+use Silex\Provider\UrlGeneratorServiceProvider;
+use Silex\WebTestCase as SilexWebTestCase;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\Security\Core\Encoder\PlaintextPasswordEncoder;
+
+class NullUserProviderTest extends SilexWebTestCase
+{
+    public function createApplication()
+    {
+        $app = new Application();
+
+        $app->register(new DoctrineServiceProvider());
+        $app->register(new FormServiceProvider());
+        $app->register(new OAuth2ServiceProvider());
+        $app->register(new SecurityServiceProvider());
+        $app->register(new SessionServiceProvider());
+        $app->register(new TwigServiceProvider());
+        $app->register(new UrlGeneratorServiceProvider());
+
+        // Return an instance of Doctrine ORM entity manager.
+        $app['authbucket_oauth2.orm'] = $app->share(function ($app) {
+            $conn = $app['dbs']['default'];
+            $event_manager = $app['dbs.event_manager']['default'];
+
+            $driver = new AnnotationDriver(new AnnotationReader(), array(__DIR__ . '/../src/AuthBucket/OAuth2/Tests/Entity'));
+
+            $config = Setup::createConfiguration(false);
+            $config->setMetadataDriverImpl($driver);
+            $config->setMetadataCacheImpl(new ArrayCache());
+            $config->setQueryCacheImpl(new ArrayCache());
+
+            return EntityManager::create($conn, $config, $event_manager);
+        });
+
+        // Fake lib dev, simply use plain text encoder.
+        $app['security.encoder.digest'] = $app->share(function ($app) {
+            return new PlaintextPasswordEncoder();
+        });
+
+        // Add model managers from ORM.
+        $app['authbucket_oauth2.model_manager.factory'] = $app->share(function ($app) {
+            return new ModelManagerFactory($app['authbucket_oauth2.orm'], $app['authbucket_oauth2.model']);
+        });
+
+        require __DIR__ . '/../../../../app/config/config_test.php';
+        require __DIR__ . '/../../../../app/config/routing.php';
+
+        return $app;
+    }
+
+    public function testNullUserProvider()
+    {
+        $parameters = array(
+            'grant_type' => 'password',
+            'username' => 'demousername3',
+            'password' => 'demopassword3',
+            'scope' => 'demoscope1 demoscope2 demoscope3',
+            'state' => 'demostate1',
+        );
+        $server = array(
+            'PHP_AUTH_USER' => 'http://democlient3.com/',
+            'PHP_AUTH_PW' => 'demosecret3',
+        );
+        $client = $this->createClient();
+        $crawler = $client->request('POST', '/oauth2/token', $parameters, array(), $server);
+        $this->assertEquals(500, $client->getResponse()->getStatusCode());
+        $this->assertNotNull(json_decode($client->getResponse()->getContent()));
+        $token_response = json_decode($client->getResponse()->getContent(), true);
+        $this->assertEquals('server_error', $token_response['error']);
+    }
+}