Fix json encode null

[datlechin]

Fix json encode null in php8.3

Fixes #0000

Changes proposed in this pull request:

Reviewers should focus on:

Screenshot

Confirmed

• [ ] Frontend changes: tested on a local Flarum installation.
• [ ] Backend changes: tests are green (run composer test).

Required changes:

• [ ] Related Flarum core extension PR's: (Omit this section if irrelevant)

[luceos]

@DavideIadeluca if you want to do an optimization, although just a slight one, stop early instead of accessing the settings repository first (which you then don't need for an admin):

        if ($this->user->isAdmin()) return;

        return json_decode(
                $settings->get('fof-gamification.autoAssignGroups', '[]'),
                true
        );

[DavideIadeluca]

@DavideIadeluca if you want to do an optimization, although just a slight one, stop early instead of accessing the settings repository first (which you then don't need for an admin):

        if ($this->user->isAdmin()) return;

        return json_decode(
                $settings->get('fof-gamification.autoAssignGroups', '[]'),
                true
        );

Yeah right, makes sense. @datlechin Can you please use the suggestion of @luceos instead? 🙏