TypeError: Drupal\field_redirect\Service\UtilityService::toArray(): Argument #1 ($mappings_string) must be of type string, null given.

Problem/Motivation

I'm getting the following error with Drupal 10 and PHP 8.

TypeError: Drupal\field_redirect\Service\UtilityService::toArray(): Argument #1 ($mappings_string) must be of type string, null given.

Steps to reproduce

• Install module
• Navigate to the module configuration page. (/admin/config/search/field-redirect)
• Try to save the form without any data
• you will get TypeError: Drupal\field_redirect\Service\UtilityService::toArray(): Argument #1 ($mappings_string) must be of type string, null given.

Proposed resolution

Causing this issue because of passing a null value.
solution 1:

    $this->settings
      ->set(UtilityService::MODULE_NAME . '.mappings', $this->utility->toArray($form_state->getValue('mappings', '')))
      ->save();

To

    $mappings = $form_state->getValue('mappings') ?? '';
    $this->settings
      ->set(UtilityService::MODULE_NAME . '.mappings', $this->utility->toArray($mappings))
      ->save();

Solution 2:
Add the required option to "The redirect mapping settings of entity (type and bundle) and fields" field.