diff --git a/core/modules/book/src/Form/BookSettingsForm.php b/core/modules/book/src/Form/BookSettingsForm.php
index 29590ccdb5..6f25078cbf 100644
--- a/core/modules/book/src/Form/BookSettingsForm.php
+++ b/core/modules/book/src/Form/BookSettingsForm.php
@@ -45,7 +45,6 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#options' => $types,
       '#required' => TRUE,
     ];
-    $form['array_filter'] = ['#type' => 'value', '#value' => TRUE];
 
     return parent::buildForm($form, $form_state);
   }
@@ -54,7 +53,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    $child_type = $form_state->getValue('book_child_type');
+    $child_type = array_filter($form_state->getValue('book_child_type'));
     if ($form_state->isValueEmpty(['book_allowed_types', $child_type])) {
       $form_state->setErrorByName('book_child_type', $this->t('The content type for the %add-child link must be one of those selected as an allowed book outline type.', ['%add-child' => $this->t('Add child page')]));
     }
@@ -74,7 +73,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     $this->config('book.settings')
     // Remove unchecked types.
       ->set('allowed_types', $allowed_types)
-      ->set('child_type', $form_state->getValue('book_child_type'))
+      ->set('child_type', array_filter($form_state->getValue('book_child_type')))
       ->save();
 
     parent::submitForm($form, $form_state);