Undefined index: Content-Type in /oauth2/client.php

[oTTa]

Notice: Undefined index: Content-Type in /var/www/html/libraries/joomla/oauth2/client.php on line 83

vardump $response

object(JHttpResponse)#367 (3) { ["code"]=> int(200) ["headers"]=> array(0) { } ["body"]=> string(523) "HTTP/1.1 400 Bad Request Vary: X-Origin Content-Type: application/json; charset=UTF-8 Date: Wed, 11 Oct 2017 16:12:26 GMT Expires: Wed, 11 Oct 2017 16:12:26 GMT Cache-Control: private, max-age=0 X-Content-Type-Options: nosniff X-Frame-Options: SAMEORIGIN X-XSS-Protection: 1; mode=block Server: GSE Alt-Svc: quic=":443"; ma=2592000; v="39,38,37,35" Accept-Ranges: none Vary: Origin,Accept-Encoding Transfer-Encoding: chunked { "error": "invalid_grant", "error_description": "Code was already redeemed." } " }