diff --git a/src/Form/GroupDeleteConfirm.php b/src/Form/GroupDeleteConfirm.php
index 38deff22a1d84dbe615e86fa364299af0677735a..26ddbc45b3e2bf340ba4963447155c2b0a3b3590 100644
--- a/src/Form/GroupDeleteConfirm.php
+++ b/src/Form/GroupDeleteConfirm.php
@@ -31,7 +31,7 @@ class GroupDeleteConfirm extends FormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, BrowserTypeInterface $paragraphs_browser_type = null, $group_machine_name = '') {
+  public function buildForm(array $form, FormStateInterface $form_state, ?BrowserTypeInterface $paragraphs_browser_type = NULL, $group_machine_name = '') {
     $this->entity = $paragraphs_browser_type;
 
     $form['id'] = array('#type' => 'hidden', '#value' => $group_machine_name);
diff --git a/src/Form/GroupEditForm.php b/src/Form/GroupEditForm.php
index 5116dcdb5e148c13dc38ac68c4ef4d449d024199..a760199b6d3d0ed1dda298210b026b2f31321fdf 100644
--- a/src/Form/GroupEditForm.php
+++ b/src/Form/GroupEditForm.php
@@ -37,7 +37,7 @@ class GroupEditForm extends FormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, BrowserTypeInterface $paragraphs_browser_type = null, $group_machine_name = '') {
+  public function buildForm(array $form, FormStateInterface $form_state, ?BrowserTypeInterface $paragraphs_browser_type = NULL, $group_machine_name = '') {
     /** @var BrowserType $paragraphs_browser_type */
     $this->entity = $paragraphs_browser_type;
     /** @var BrowserGroupList $groups */
diff --git a/src/Form/ParagraphTypeGroupsForm.php b/src/Form/ParagraphTypeGroupsForm.php
index 40a4854f9f80dae39257fb144928bc53aa7e3515..5a49301eb103461b42b3b79419e3835ca59e2dd7 100644
--- a/src/Form/ParagraphTypeGroupsForm.php
+++ b/src/Form/ParagraphTypeGroupsForm.php
@@ -76,7 +76,7 @@ class ParagraphTypeGroupsForm extends FormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, ParagraphsTypeInterface $paragraphs_type = null) {
+  public function buildForm(array $form, FormStateInterface $form_state, ?ParagraphsTypeInterface $paragraphs_type = NULL) {
     $paragraph_browser_type_ids = $this->entityTypeManager->getStorage('paragraphs_browser_type')->getQuery()->accessCheck(TRUE)->execute();
     //@todo: on unsaved change, hide links to configuration forms.
     if(!$paragraph_browser_type_ids) {
diff --git a/src/Form/ParagraphsBrowserForm.php b/src/Form/ParagraphsBrowserForm.php
index 7fa0822f9fcd4aad03fd509d08688ed340623ed1..3cf3cd1b1dcd46f14d51517ca27ba998ab616a89 100644
--- a/src/Form/ParagraphsBrowserForm.php
+++ b/src/Form/ParagraphsBrowserForm.php
@@ -10,16 +10,16 @@ namespace Drupal\paragraphs_browser\Form;
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Ajax\AjaxResponse;
 use Drupal\Core\Ajax\CloseModalDialogCommand;
-use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\File\FileUrlGeneratorInterface;
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Session\AccountInterface;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\paragraphs_browser\Ajax\AddParagraphTypeCommand;
 use Symfony\Component\DependencyInjection\ContainerInterface;
-use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Session\AccountInterface;
 
 /**
  * Class CleanupUrlAliases.
@@ -67,18 +67,20 @@ class ParagraphsBrowserForm extends FormBase {
   protected $fileUrlGenerator;
 
   /**
-   * Constructs a new ParagraphsTypeDeleteConfirm object.
+   * Constructs a new ParagraphsBrowserForm object.
    *
    * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
-   *
+   *   The entity type manager.
    * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
-   *
+   *   The entity type bundle info.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
-   *   The module handler service.
+   *   The module handler.
    * @param \Drupal\Core\Session\AccountInterface $current_user
    *   The current user.
+   * @param \Drupal\Core\File\FileUrlGeneratorInterface|null $file_url_generator
+   *   The file URL generator.
    */
-  public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityTypeBundleInfoInterface $entity_type_bundle_info, ModuleHandlerInterface $module_handler, AccountInterface $current_user, FileUrlGeneratorInterface $file_url_generator = NULL) {
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityTypeBundleInfoInterface $entity_type_bundle_info, ModuleHandlerInterface $module_handler, AccountInterface $current_user, ?FileUrlGeneratorInterface $file_url_generator = NULL) {
     $this->entityTypeManager = $entity_type_manager;
     $this->entityTypeBundleInfo = $entity_type_bundle_info;
     $this->moduleHandler = $module_handler;
@@ -109,7 +111,7 @@ class ParagraphsBrowserForm extends FormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, FieldConfig $field_config = null, $paragraphs_browser_type = null, $uuid = null) {
+  public function buildForm(array $form, FormStateInterface $form_state, ?FieldConfig $field_config = null, $paragraphs_browser_type = null, $uuid = null) {
     $form_state->addBuildInfo('uuid', $uuid);
 
     $form['#attached']['library'][] = 'paragraphs_browser/modal';