[13.x] allow null to be passed directly to redirectGuestsTo()

[timmylindh]

Following #59505, which updated the exception handler to respect a null redirect and return a 401 response instead of forcing a redirect to route('login'), the redirectGuestsTo() method still does not accept null in its type signature.

This means API-only apps that want to disable the redirect must use:

$middleware->redirectGuestsTo(fn () => null);

With this change, you can now pass null directly:

$middleware->redirectGuestsTo(null);

Changes

• Updated redirectGuestsTo() type signature from callable|string to callable|string|null
• Updated redirectTo() to wrap null in a closure (same as it already does for strings), so it properly propagates through redirectUsing()

Backward Compatibility

This is fully backward compatible. Existing calls with callable or string arguments are unaffected. The only new behavior is that null is now a valid argument.