Fix issue with sending empty Bearer value as Authorization header

Author: inserve-paul

src/Client/APIClient.php

@@ -181,8 +181,8 @@ protected function getDefaultHeaders(): array
             'Content-Type' => 'application/json',
         ];
 
-        if ($this->accessToken !== null) {
-            $headers['Authorization'] = sprintf('Bearer %s', $this->accessToken->getAccessToken() ?? '');
+        if ($this->accessToken?->getAccessToken()) {
+            $headers['Authorization'] = sprintf('Bearer %s', $this->accessToken->getAccessToken());
         }
 
         return $headers;