PHP fatal error on activation

When we installed the module in Drupal 11, the following error occurred:

PHP Fatal error:  Type of Drupal\migrate_wizard\Form\BaseFormFields::$typedConfigManager 
must be Drupal\Core\Config\TypedConfigManagerInterface (as in class Drupal\Core\Form\ConfigFormBase)
This happened because Drupal 11 enforces stricter type-checking. The BaseFormFields class extends ConfigFormBase, which already defines $typedConfigManager as an instance of TypedConfigManagerInterface.

However, in the module's code, the property was declared without a type:

protected $typedConfigManager = NULL;

This meant that when Drupal tried to validate the type against the parent class (ConfigFormBase), it found a mismatch, causing the fatal error.

Please review.
Thanks