diff --git a/src/OpenIDConnectClient.php b/src/OpenIDConnectClient.php
index adabf80c..ee3c971d 100644
--- a/src/OpenIDConnectClient.php
+++ b/src/OpenIDConnectClient.php
@@ -1221,10 +1221,9 @@ protected function urlEncode(string $str): string
     /**
      * @param string $jwt encoded JWT
      * @param int $section the section we would like to decode
-     * @return object
+     * @return object|null
      */
-    protected function decodeJWT(string $jwt, int $section = 0): stdClass {
-
+    protected function decodeJWT(string $jwt, int $section = 0) {
         $parts = explode('.', $jwt);
         return json_decode(base64url_decode($parts[$section]), false);
     }
@@ -1725,7 +1724,10 @@ public function getAccessToken(): string
         return $this->accessToken;
     }
 
-    public function getRefreshToken(): string
+    /**
+     * @return string|null
+     */
+    public function getRefreshToken()
     {
         return $this->refreshToken;
     }
diff --git a/tests/OpenIDConnectClientTest.php b/tests/OpenIDConnectClientTest.php
index f895879c..793c320f 100644
--- a/tests/OpenIDConnectClientTest.php
+++ b/tests/OpenIDConnectClientTest.php
@@ -7,9 +7,22 @@
 
 class OpenIDConnectClientTest extends TestCase
 {
-    /**
-     * @return void
-     */
+    public function testJWTDecode()
+    {
+        $client = new OpenIDConnectClient();
+        $client->setAccessToken('');
+        $header = $client->getAccessTokenHeader();
+        self::assertEquals('', $header);
+    }
+
+    public function testGetNullRefreshToken()
+    {
+        $client = new OpenIDConnectClient();
+        $client->setAccessToken('');
+        $token = $client->getRefreshToken();
+        self::assertEquals('', $token);
+    }
+
     public function testGetRedirectURL()
     {
         $client = new OpenIDConnectClient();