$tokenResponse type declaration bug

[MaximumRGB]

Hello. It seems there's a mistake in $tokenResponse type declaration (string instead of mixed):

/**
  * @var string stores the token response
  */
private $tokenResponse;

... $token_json = $this->requestTokens($code); ... $this->tokenResponse = $token_json; ...

 /**
  * Requests ID and Access tokens
  *
  * @param string $code
  * @return mixed
  * @throws OpenIDConnectClientException
  */
protected function requestTokens($code)