REST API: Treat null and other falsy values like `false` in 'rest_allow_anonymous_comments'

[jnylen0]

Currently the rest_allow_anonymous_comments filter checks for an explicit false value to disable anonymous comments. We should extend this check to any falsy value instead.

As noted in the tests, the specific case I'm envisioning is that a plugin developer forgets to include a return value for some code path in their callback for this filter, leading to a value of null which is currently treated like true. We should fix this before it has a chance to show up in the wild.

Props @joehoyle for originally spotting this at ticket:38855#comment:6, but it wasn't addressed in the commit there.

[jnylen0]

@rachelbaker if we don't fix this in 4.7, is it something that we can still go back and fix later?

[rachelbaker]

Patch 39010.diff​ looks good. @jnylen0 you want to commit when ready?

[jnylen0]

In 39487:

REST API: Treat any falsy value as false in 'rest_allow_anonymous_comments'.

Extend the check in 'rest_allow_anonymous_comments' to accept any falsy value
(previously this was an explicit check for false).

One possible failure case is that a plugin developer forgets to include a
return value for some code path in their callback for this filter, leading to a
value of null which is currently treated like true.

Props joehoyle, jnylen0.

Fixes #39010.

[jnylen0]

Needs merge to 4.7.1 after the 4.7 release.

[jnylen0]

Making this ticket great again.

[dd32]

In 39566:

REST API: Treat any falsy value as false in 'rest_allow_anonymous_comments'.

Extend the check in 'rest_allow_anonymous_comments' to accept any falsy value (previously this was an explicit check for false).

One possible failure case is that a plugin developer forgets to include a return value for some code path in their callback for this filter, leading to a value of null which is currently treated like true.

Props joehoyle, jnylen0.
Merges [39487] to the 4.7 branch.
Fixes #39010.