[Security] Use instanceof NullToken in voters

[l-vo]

To test if the user is not logged.

[l-vo]

@OskarStark changes applied, thank you :)

[javiereguiluz]

Sorry to ping you again @chalasr but could you please review if this security-related proposal is correct? Thanks.

[chalasr]

(No worry @javiereguiluz, don't hesitate!)

I'm not totally sure about this change. Technically, the current code is correct as it covers the NullToken case as well as any eventual "unauthenticated" custom token (ref https://github.com/symfony/symfony/pull/42650). With that in mind and given "use NullToken but only in voters" makes it way more complicated, I think it's better to keep the example it as-is.

Having @wouterj's point of view would be good though.

[l-vo]

Indeed... Actually I'm not sure about my change anymore 😁

[javiereguiluz]

OK, let's close this then. Thank you all for the reviews 🙏