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This check may affect code paths that were previously unaffected by this error, therefore causing a backwards-compatibility issue. I suggest adding an isset before line 574 instead:

if (!isset($this->token['expires_in'])) {
    // if the token does not have an "expires_in", then it's considered expired
    return true;
}

return ($created + ($this->token['expires_in'] - 30)) < time();

@bshaffer, agree with you. Added new changes to PR