PHP Warning: Argument #2 ($key) must be passed by reference,

[JungeG]

Hi!
I just updated to API-2.1.1-Snapshot and get following warning

PHP Warning: OAuth\Common\Http\Client\AbstractClient::OAuth\Common\Http\Client{closure}(): Argument #2 ($key) must be passed by reference, value given in phar:///etc/openhab/scripts/viessmann/Viessmann-Api-2.1.1-SNAPSHOT.phar/vendor/lusitanian/oauth/src/OAuth/Common/Http/Client/AbstractClient.php on line 70

my credentials.properties:

user=mail@mail.de
pwd=passwd
clientId=myclientid
installationId=
gatewayId=

my bootstrap.php:

`<?php

use Viessmann\API\ViessmannAPI;
use Viessmann\API\ViessmannApiException;
session_start();
include 'phar://' . DIR . '/Viessmann-Api-2.1.1-SNAPSHOT.phar/index.php';

$params = parse_ini_file(DIR . "/credentials.properties");
function print_exception($e){
echo "Message: " . $e->getMessage() . "\n";
echo "Code: " . $e->getCode() . "\n";
// echo "Trace:" . $e->getTraceAsString() . "\n";
}
;
$errorHandler= function($e)
{
$currentException=$e;
do {
print_exception($currentException);
} while ($currentException = $currentException->getPrevious());
};

set_exception_handler($errorHandler);
try {
$viessmannApi = new ViessmannAPI($params);
} catch (ViessmannApiException $e) {
$errorHandler($e);
exit();
}
`

How can I get rid of the warning or just ignore it?
Thanks Georg