diff --git a/src/Entity/AbstractTokenEntity.php b/src/Entity/AbstractTokenEntity.php
index 45140ad8..02a24d1b 100644
--- a/src/Entity/AbstractTokenEntity.php
+++ b/src/Entity/AbstractTokenEntity.php
@@ -153,10 +153,9 @@ abstract class AbstractTokenEntity
      */
     public function __toString()
     {
-        if (is_null($this->token)) {
-            throw new \BadMethodCallException('Token is null');
+        if ($this->token === null) {
+            return '';
         }
-
         return $this->token;
     }
 
diff --git a/src/Exception/UnauthorizedClientException.php b/src/Exception/UnauthorizedClientException.php
index ac3485c7..fd1f18c3 100644
--- a/src/Exception/UnauthorizedClientException.php
+++ b/src/Exception/UnauthorizedClientException.php
@@ -29,7 +29,7 @@ class UnauthorizedClientException extends OAuthException
     /**
      * {@inheritdoc}
      */
-    public function __construct($parameter)
+    public function __construct()
     {
         parent::__construct('The client is not authorized to request an access token using this method.');
     }
diff --git a/tests/Entity/AbstractTokenEntityTest.php b/tests/Entity/AbstractTokenEntityTest.php
index 2f16ea2e..3b934c0c 100644
--- a/tests/Entity/AbstractTokenEntityTest.php
+++ b/tests/Entity/AbstractTokenEntityTest.php
@@ -74,7 +74,7 @@ class AbstractTokenTest extends \PHPUnit_Framework_TestCase
         $accessTokenStorage->shouldReceive('getScopes')->andReturn(
             []
         );
-        $accessTokenStorage->shouldReceive('setServer');
+        $accessTokenStorage''>shouldReceive('setServer');
 
         $server->setAccessTokenStorage($accessTokenStorage);
 
@@ -103,4 +103,14 @@ class AbstractTokenTest extends \PHPUnit_Framework_TestCase
         $this->assertTrue($result['scope1'] instanceof ScopeEntity);
         $this->assertTrue($result['scope2'] instanceof ScopeEntity);
     }
+
+    public function test__toString()
+    {
+        $server = M::mock('League\OAuth2\Server\AbstractServer');
+
+        $entity = new StubAbstractTokenEntity($server);
+        $this->assertEquals('', (string) $entity);
+        $entity->setToken('foobar');
+        $this->assertEquals('foobar', (string) $entity);
+    }
 }
diff --git a/tests/Grant/ClientCredentialsGrantTest.php b/tests/Grant/ClientCredentialsGrantTest.php
index be01da8b..8db12085 100644
--- a/tests/Grant/ClientCredentialsGrantTest.php
+++ b/tests/Grant/ClientCredentialsGrantTest.php
@@ -198,4 +198,55 @@ class ClientCredentialsGrantTest extends \PHPUnit_Framework_TestCase
         $server->addGrantType($grant);
         $server->issueAccessToken();
     }
+
+    public function testClientNotAuthorizedToUseGrant()
+    {
+        $this->setExpectedException('\League\OAuth2\Server\Exception\UnauthorizedClientException');
+
+        $_POST = [
+            'grant_type' => 'client_credentials',
+            'client_id' =>  'testapp',
+            'client_secret' =>  'foobar',
+            'scope' =>  'foo'
+        ];
+
+        $server = new AuthorizationServer;
+        $grant = new ClientCredentialsGrant;
+
+        $clientStorage = M::mock('League\OAuth2\Server\Storage\ClientInterface');
+        $clientStorage->shouldReceive('setServer');
+        $clientStorage->shouldReceive('get')->andThrow(
+            new \League\OAuth2\Server\Exception\UnauthorizedClientException
+        );
+
+        $sessionStorage = M::mock('League\OAuth2\Server\Storage\SessionInterface');
+        $sessionStorage->shouldReceive('setServer');
+        // $sessionStorage->shouldReceive('create')->andreturn(123);
+        // $sessionStorage->shouldReceive('getScopes')->shouldReceive('getScopes')->andReturn([
+        //     (new ScopeEntity($server))->setId('foo')
+        // ]);
+        // $sessionStorage->shouldReceive('associateScope');
+
+        $accessTokenStorage = M::mock('League\OAuth2\Server\Storage\AccessTokenInterface');
+        $accessTokenStorage->shouldReceive('setServer');
+        // $accessTokenStorage->shouldReceive('create');
+        // $accessTokenStorage->shouldReceive('getScopes')->andReturn([
+        //     (new ScopeEntity($server))->setId('foo')
+        // ]);
+        // $accessTokenStorage->shouldReceive('associateScope');
+
+        $scopeStorage = M::mock('League\OAuth2\Server\Storage\ScopeInterface');
+        $scopeStorage->shouldReceive('setServer');
+        $scopeStorage->shouldReceive('get')->andReturn(
+            (new ScopeEntity($server))->setId('foo')
+        );
+
+        $server->setClientStorage($clientStorage);
+        $server->setScopeStorage($scopeStorage);
+        $server->setSessionStorage($sessionStorage);
+        $server->setAccessTokenStorage($accessTokenStorage);
+
+        $server->addGrantType($grant);
+        $server->issueAccessToken();
+    }
 }