prepareBody example

    public static function create(callable $handler = null): self
    {
        $stack = new self($handler ?: Utils::chooseHandler());
        $stack->push(Middleware::httpErrors(), 'http_errors');
        $stack->push(Middleware::redirect(), 'allow_redirects');
        $stack->push(Middleware::cookies(), 'cookies');
        $stack->push(Middleware::prepareBody(), 'prepare_body');

        return $stack;
    }

    /** * @param (callable(RequestInterface, array): PromiseInterface)|null $handler Underlying HTTP handler. */
    public function __construct(callable $handler = null)
    {
        $this->handler = $handler;
    }