Issue #3509056: PHP 8.4 implicit nullable deprecation

Closes #3509056

src/Form/FieldValidationRuleAddForm.php

@@ -50,7 +50,7 @@ class FieldValidationRuleAddForm extends FieldValidationRuleFormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, FieldValidationRuleSetInterface $field_validation_rule_set = NULL, $field_validation_rule = NULL, $field_name = '') {
+  public function buildForm(array $form, FormStateInterface $form_state, ?FieldValidationRuleSetInterface $field_validation_rule_set = NULL, $field_validation_rule = NULL, $field_name = '') {
     $form = parent::buildForm($form, $form_state, $field_validation_rule_set, $field_validation_rule);
 
     $form['#title'] = $this->t('Add %label field validation rule', ['%label' => $this->fieldValidationRule->label()]);