Steps to reproduce the issue

Install nightly staging
Under Content > Fields, create a custom field.

Actual result

Error decoding JSON data: Syntax error
\libraries\vendor\joomla\registry\src\Format\Json.php:72

# | Function | Location
-- | -- | --
1 | () | JROOT\libraries\vendor\joomla\registry\src\Format\Json.php:72
2 | Joomla\Registry\Format\Json->stringToObject() | JROOT\libraries\vendor\joomla\registry\src\Registry.php:370
3 | Joomla\Registry\Registry->loadString() | JROOT\administrator\components\com_fields\models\field.php:334
4 | FieldsModelField->getItem() | JROOT\libraries\src\MVC\View\HtmlView.php:423
5 | Joomla\CMS\MVC\View\HtmlView->get() | JROOT\administrator\components\com_fields\views\field\view.html.php:52
6 | FieldsViewField->display() | JROOT\libraries\src\MVC\Controller\BaseController.php:672
7 | Joomla\CMS\MVC\Controller\BaseController->display() | JROOT\administrator\components\com_fields\controller.php:57
8 | FieldsController->display() | JROOT\libraries\src\MVC\Controller\BaseController.php:710
9 | Joomla\CMS\MVC\Controller\BaseController->execute() | JROOT\administrator\components\com_fields\fields.php:29
10 | require_once() | JROOT\libraries\src\Component\ComponentHelper.php:382
11 | Joomla\CMS\Component\ComponentHelper::executeComponent() | JROOT\libraries\src\Component\ComponentHelper.php:357
12 | Joomla\CMS\Component\ComponentHelper::renderComponent() | JROOT\libraries\src\Application\AdministratorApplication.php:101
13 | Joomla\CMS\Application\AdministratorApplication->dispatch() | JROOT\libraries\src\Application\AdministratorApplication.php:159
14 | Joomla\CMS\Application\AdministratorApplication->doExecute() | JROOT\libraries\src\Application\CMSApplication.php:195
15 | Joomla\CMS\Application\CMSApplication->execute() | JROOT\administrator\index.php:51

System information (as much as possible)

nightly staging