Response construct use property promotion

[joanhey]

Also fix a problem with the last __construct, that permit array|null in $headers and later this will break.

Before:

protected array $headers = [];

    /**
     * Response constructor.
     *
     * @param int $status
     * @param array|null $headers
     * @param string $body
     */
 public function __construct(
        int     $status = 200,
        ?array  $headers = [],
        string  $body = ''
    )
    {
        $this->status = $status;
        $this->headers = $headers;
        $this->body = $body;
    }

$this->headers = $headers; will break if we send a null.

And if we permit null, we have more problems in the class.

Example:

public function getHeaders(): array
    {
        return $this->headers;
    }
...

[joanhey]

Curiously was passing the tests, than use null. 😮

@walkor you can decide how do you want it.

We can also check in the constructor if is a null to be converted to array().

EDIT: the fail is from the static analyzer phpstan, not the unit tests

[walkor]

I agree with your PR