Can't add a layout with this.

Problem/Motivation

Tried adding a layout using this and i get:

TypeError: Argument 1 passed to Drupal\Core\Render\Element::children() must be of the type array, null given, called in E:\www\myssc\html\core\modules\layout_discovery\layout_discovery.module on line 44 in Drupal\Core\Render\Element::children() (line 72 of E:\www\myssc\html\core\lib\Drupal\Core\Render\Element.php)

#0 E:\www\myssc\html\core\modules\layout_discovery\layout_discovery.module(44): Drupal\Core\Render\Element::children(NULL)
#1 E:\www\myssc\html\core\lib\Drupal\Core\Theme\ThemeManager.php(293): template_preprocess_layout(Array, 'css_grid', Array)
#2 E:\www\myssc\html\core\lib\Drupal\Core\Render\Renderer.php(436): Drupal\Core\Theme\ThemeManager->render('css_grid', Array)
#3 E:\www\myssc\html\core\lib\Drupal\Core\Render\Renderer.php(449): Drupal\Core\Render\Renderer->doRender(Array)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes