diff --git a/src/Tree/EntityTreeBuilder.php b/src/Tree/EntityTreeBuilder.php
index c701c9938822e29c4dc82b9cc29e1fd0c1b4ae50..52a063acc228e9ad8bcae315e5beac84da817b03 100644
--- a/src/Tree/EntityTreeBuilder.php
+++ b/src/Tree/EntityTreeBuilder.php
@@ -35,14 +35,19 @@ class EntityTreeBuilder implements TreeBuilderInterface {
    *
    * @param string $entityType
    *   The type of the entity.
-   *
    * @param string $bundleID
    *   The bundle ID.
+   * @param string|null $langCode
+   *   The language code.
+   * @param int $parent
+   *   The parent entity ID.
+   * @param int|null $max_depth
+   *   The maximum depth of the tree.
    *
    * @return array
    *   All entities in the entity bundle.
    */
-  public function loadTree(string $entityType, string $bundleID, string $langCode = NULL, int $parent = 0, int $max_depth = NULL) {
+  public function loadTree(string $entityType, string $bundleID, ?string $langCode = NULL, int $parent = 0, ?int $max_depth = NULL) {
     if ($this->hasAccess()) {
       if ($bundleID === '*') {
         // Load all entities regardless bundles.
@@ -148,14 +153,14 @@ class EntityTreeBuilder implements TreeBuilderInterface {
   /**
    * Check if a user has the access to the tree.
    *
-   * @param \Drupal\Core\Session\AccountProxyInterface $user
+   * @param \Drupal\Core\Session\AccountProxyInterface|null $user
    *   The user object to check.
    *
    * @return bool
    *   If the user has the access to the tree return TRUE,
    *   otherwise return FALSE.
    */
-  private function hasAccess(AccountProxyInterface $user = NULL) {
+  private function hasAccess(?AccountProxyInterface $user = NULL) {
     // Check current user as default.
     if (empty($user)) {
       $user = \Drupal::currentUser();
diff --git a/src/Tree/TaxonomyTreeBuilder.php b/src/Tree/TaxonomyTreeBuilder.php
index b106379b5942f33981e096c3611a248855699cbd..8e2ad2695425fb6c411392abc3da7f0bca693cf2 100644
--- a/src/Tree/TaxonomyTreeBuilder.php
+++ b/src/Tree/TaxonomyTreeBuilder.php
@@ -34,14 +34,19 @@ class TaxonomyTreeBuilder implements TreeBuilderInterface {
    *
    * @param string $entityType
    *   The type of the entity.
-   *
    * @param string $bundleID
    *   The bundle ID.
+   * @param string|null $langCode
+   *   The language code.
+   * @param int $parent
+   *   The parent entity ID.
+   * @param int|null $max_depth
+   *   The maximum depth of the tree.
    *
    * @return array
    *   All entities in the entity bundle.
    */
-  public function loadTree(string $entityType, string $bundleID, string $langCode = NULL, int $parent = 0, int $max_depth = NULL) {
+  public function loadTree(string $entityType, string $bundleID, ?string $langCode = NULL, int $parent = 0, ?int $max_depth = NULL) {
     // Setup the language code for this tree.
     // Use current language by default.
     if (empty($langCode)) {
@@ -126,14 +131,14 @@ class TaxonomyTreeBuilder implements TreeBuilderInterface {
   /**
    * Check if a user has the access to the tree.
    *
-   * @param \Drupal\Core\Session\AccountProxyInterface $user
+   * @param \Drupal\Core\Session\AccountProxyInterface|null $user
    *   The user object to check.
    *
    * @return bool
    *   If the user has the access to the tree return TRUE,
    *   otherwise return FALSE.
    */
-  private function hasAccess(AccountProxyInterface $user = NULL) {
+  private function hasAccess(?AccountProxyInterface $user = NULL) {
     // Check current user as default.
     if (empty($user)) {
       $user = \Drupal::currentUser();
diff --git a/src/Tree/TreeBuilderInterface.php b/src/Tree/TreeBuilderInterface.php
index 356f9c176f3b1e67120d136a21215cb4e1ab00b0..5a01e0e6806fbf2c9067e7cfa50b33ddd41b8fd3 100644
--- a/src/Tree/TreeBuilderInterface.php
+++ b/src/Tree/TreeBuilderInterface.php
@@ -14,14 +14,19 @@ interface TreeBuilderInterface {
    *
    * @param string $entityType
    *   The type of the entity.
-   *
    * @param string $bundleID
    *   The bundle ID.
+   * @param string|null $langCode
+   *   The language code.
+   * @param int $parent
+   *   The parent entity ID.
+   * @param int|null $max_depth
+   *   The maximum depth of the tree.
    *
    * @return array
    *   All entities in the entity bundle.
    */
-  public function loadTree(string $entityType, string $bundleID, string $langCode = NULL, int $parent = 0, int $max_depth = NULL);
+  public function loadTree(string $entityType, string $bundleID, ?string $langCode = NULL, int $parent = 0, ?int $max_depth = NULL);
 
   /**
    * Create a tree node.