class Guard
{

    ...

    public function __construct($tokenGetter = null, $signer = null)
    {
        $this->signer = $signer ?? new Sha256();
        $this->tokenGetter = $tokenGetter ?? app(TokenGetter::class);
    }

    public function user() :? UserContract
    {
        if (is_null($this->user) === false) {
            return $this->user;
        }

        try {
            $token = $this->resolveToken($this->tokenGetter->getToken());
        } catch (TokenNotPresentException $ex) {
            return null;
        }

        $this->claims = $token->getClaims();

        return $this->user = $token->getUser();
    }

    ...

}