diff --git a/src/Grant/PasswordGrant.php b/src/Grant/PasswordGrant.php
index f9298722..a2ce660b 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -72,12 +72,12 @@ class PasswordGrant extends AbstractGrant
     {
         $username = $this->getRequestParameter('username', $request);
         if (is_null($username)) {
-            throw OAuthServerException::invalidRequest('username', null, '`%s` parameter is missing');
+            throw OAuthServerException::invalidRequest('username', '`%s` parameter is missing');
         }
 
         $password = $this->getRequestParameter('password', $request);
         if (is_null($password)) {
-            throw OAuthServerException::invalidRequest('password', null, '`%s` parameter is missing');
+            throw OAuthServerException::invalidRequest('password', '`%s` parameter is missing');
         }
 
         $user = $this->userRepository->getUserEntityByUserCredentials($username, $password);
diff --git a/src/Grant/RefreshTokenGrant.php b/src/Grant/RefreshTokenGrant.php
index 04d078e4..a03bdc90 100644
--- a/src/Grant/RefreshTokenGrant.php
+++ b/src/Grant/RefreshTokenGrant.php
@@ -101,7 +101,7 @@ class RefreshTokenGrant extends AbstractGrant
     {
         $encryptedRefreshToken = $this->getRequestParameter('refresh_token', $request);
         if (is_null($encryptedRefreshToken)) {
-            throw OAuthServerException::invalidRequest('refresh_token', null, '`%s` parameter is missing');
+            throw OAuthServerException::invalidRequest('refresh_token', '`%s` parameter is missing');
         }
 
         // Validate refresh token