0a1,13
> diff --git a/core/lib/Drupal/Core/Render/Element/Checkbox.php b/core/lib/Drupal/Core/Render/Element/Checkbox.php
> index 9092314dfd..6f75b0482b 100644
> --- a/core/lib/Drupal/Core/Render/Element/Checkbox.php
> +++ b/core/lib/Drupal/Core/Render/Element/Checkbox.php
> @@ -52,7 +52,7 @@ public function getInfo() {
>     * {@inheritdoc}
>     */
>    public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
> -    if ($input === FALSE) {
> +    if ($input === FALSE || is_null($input)) {
>        // Use #default_value as the default value of a checkbox, except change
>        // NULL to 0, because FormBuilder::handleInputElement() would otherwise
>        // replace NULL with empty string, but an empty string is a potentially
2c15
< index 35611fd..97f2147 100644
---
> index 35611fd3b9..97f2147259 100644