diff --git a/src/Form/LikeForm.php b/src/Form/LikeForm.php
index 529c28b10915d38fc335df38ae174a6c3b9aaf9c..76a63d554f5c0d199b38b2913aa06881f547e0bf 100644
--- a/src/Form/LikeForm.php
+++ b/src/Form/LikeForm.php
@@ -62,7 +62,7 @@ class LikeForm extends FormBase {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, FieldItemInterface $item = NULL, array $settings = []) {
+  public function buildForm(array $form, FormStateInterface $form_state, ?FieldItemInterface $item = NULL, array $settings = []) {
     $entity = $item->getEntity();
     $form['#item'] = $item;
     $form['#theme'] = 'like_form';
diff --git a/src/LikeHelper.php b/src/LikeHelper.php
index fd56daf2e3d34117ad36ee70a288963d88a21145..c8c2043c2bdfb6d297c4cad7f0a6317713302779 100644
--- a/src/LikeHelper.php
+++ b/src/LikeHelper.php
@@ -77,7 +77,7 @@ class LikeHelper implements LikeHelperInterface {
   /**
    * {@inheritdoc}
    */
-  public function like(EntityInterface $entity, AccountInterface $user = NULL) {
+  public function like(EntityInterface $entity, ?AccountInterface $user = NULL) {
     if (empty($user)) {
       $user = $this->currentUser;
     }
@@ -123,7 +123,7 @@ class LikeHelper implements LikeHelperInterface {
   /**
    * {@inheritdoc}
    */
-  public function unlike(EntityInterface $entity, AccountInterface $user = NULL) {
+  public function unlike(EntityInterface $entity, ?AccountInterface $user = NULL) {
     if (empty($user)) {
       $user = $this->currentUser;
     }
@@ -177,7 +177,7 @@ class LikeHelper implements LikeHelperInterface {
   /**
    * {@inheritdoc}
    */
-  public function userHasLiked(EntityInterface $entity, AccountInterface $user = NULL):bool {
+  public function userHasLiked(EntityInterface $entity, ?AccountInterface $user = NULL):bool {
     if (empty($user)) {
       $user = $this->currentUser;
     }
diff --git a/src/LikeHelperInterface.php b/src/LikeHelperInterface.php
index 3315c0d0620d955ce162c79071c78c920de7772d..5bc02e504b55de5ee5a0db284bdc2a89b100c62f 100644
--- a/src/LikeHelperInterface.php
+++ b/src/LikeHelperInterface.php
@@ -22,7 +22,7 @@ interface LikeHelperInterface {
    * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
    * @throws \Drupal\Core\Entity\EntityStorageException
    */
-  public function like(EntityInterface $entity, AccountInterface $user = NULL);
+  public function like(EntityInterface $entity, ?AccountInterface $user = NULL);
 
   /**
    * Undoes a like.
@@ -36,7 +36,7 @@ interface LikeHelperInterface {
    * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
    * @throws \Drupal\Core\Entity\EntityStorageException
    */
-  public function unlike(EntityInterface $entity, AccountInterface $user = NULL);
+  public function unlike(EntityInterface $entity, ?AccountInterface $user = NULL);
 
   /**
    * Checks whether a user has liked an entity.
@@ -52,7 +52,7 @@ interface LikeHelperInterface {
    * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
    * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
    */
-  public function userHasLiked(EntityInterface $entity, AccountInterface $user = NULL):bool;
+  public function userHasLiked(EntityInterface $entity, ?AccountInterface $user = NULL):bool;
 
   /**
    * Get num of likes.