[10.x] phpdoc: Auth\Access\Response constructor allows null message

[snmatsui]

Problem

Response::allow() and Response::deny() construct Response with a null $message.
However, the Response constructor's phpdoc only allows string $message.
Response::$message is passed to AuthorizationException, so a null $message creates an Exception with the default message This action is unauthorized. However, an empty string $message creates an Exception with an empty string message.

https://github.com/laravel/framework/blob/master/src/Illuminate/Auth/Access/AuthorizationException.php#L34

Solution

I modified Phpdoc to allow a null $message.

Users who get benefits from this

Users of static analysis tools (like PHPStan) would not encounter this error when using directly new Response():

Parameter #2 $message of class Illuminate\Auth\Access\Response constructor expects string, null given.

[snmatsui]

It looks like it would be desirable to change constructor $message = '' to $message = null as well,
However, considering the size of the impact, it is left unchanged here.