Fix arrayGet type exception on transport when getting errors with null body

Author: ffouchier

src/Transports/Transport.php

@@ -112,7 +112,7 @@ public function request($endpoint, array $data = [], $method = 'get')
             sprintf(
                 'The request ended on a %s code : %s',
                 $httpStatusCode,
-                $this->arrayGet($response, $this->getErrorKey()) ?? $rawResponse ?? 'Unknown error message'
+                $this->arrayGet($response ?? [], $this->getErrorKey()) ?? $rawResponse ?? 'Unknown error message'
             ),
             $httpStatusCode
         );