In current class:
namespace Atom\Http\Message\Request;
I have seen that in __construct class can receive any string, and we can also just create a class like this:
$request = new Request('any_string');
but this is wrong in my opinion, maybe we will create some array for validating this.

protected $availableMethods = ['get', 'post', 'options' ...]

and than check is method in current array in
filterMethod($method)

What do think about this?