diff --git a/src/Controller/BlocksController.php b/src/Controller/BlocksController.php
index c5b918c025edb89581dfb7ccc53ec61c78ead5dc..14f93110e79fc26b20b639ce70bb22e876272aab 100644
--- a/src/Controller/BlocksController.php
+++ b/src/Controller/BlocksController.php
@@ -40,7 +40,7 @@ private function getEditableConfig() {
   /**
    * Function to export custom blocks.
    */
-  public function exportBlocks(array $form = NULL, FormStateInterface $form_state = NULL) {
+  public function exportBlocks(?array $form = NULL, ?FormStateInterface $form_state = NULL) {
     StructureSyncHelper::logMessage('Custom blocks export started');
 
     if (is_object($form_state) && $form_state->hasValue('export_block_list')) {
@@ -109,7 +109,7 @@ public function exportBlocks(array $form = NULL, FormStateInterface $form_state
    * an array with a key value pair for form with key 'style' and value 'full',
    * 'safe' or 'force' to apply that import style.
    */
-  public function importBlocks(array $form, FormStateInterface $form_state = NULL) {
+  public function importBlocks(array $form, ?FormStateInterface $form_state = NULL) {
     StructureSyncHelper::logMessage('Custom blocks import started');
 
     // Check if the import style has been defined in the form (state) and else
diff --git a/src/Controller/MenuLinksController.php b/src/Controller/MenuLinksController.php
index c0495856fa79d2bb2f0739e3d73a7c799ad93eb3..934cd48b758263b330bfe94abc3847fc518e6feb 100644
--- a/src/Controller/MenuLinksController.php
+++ b/src/Controller/MenuLinksController.php
@@ -63,7 +63,7 @@ private function getEditableConfig() {
   /**
    * Function to export menu links.
    */
-  public function exportMenuLinks(array $form = NULL, FormStateInterface $form_state = NULL) {
+  public function exportMenuLinks(?array $form = NULL, ?FormStateInterface $form_state = NULL) {
     StructureSyncHelper::logMessage('Menu links export started');
 
     if (is_object($form_state) && $form_state->hasValue('export_menu_list')) {
@@ -166,7 +166,7 @@ public function menuTreeFlatten(array $tree) {
    * an array with a key value pair for form with key 'style' and value 'full',
    * 'safe' or 'force' to apply that import style.
    */
-  public function importMenuLinks(array $form, FormStateInterface $form_state = NULL) {
+  public function importMenuLinks(array $form, ?FormStateInterface $form_state = NULL) {
     StructureSyncHelper::logMessage('Menu links import started');
 
     // Check if the there is a selection made in a form for what menus need to
diff --git a/src/Controller/TaxonomiesController.php b/src/Controller/TaxonomiesController.php
index 112190225fc28193acc3ec0d7917080e2c2c3d26..0e38f4f6b429cdc5dffb2130998eb88042acf8fe 100644
--- a/src/Controller/TaxonomiesController.php
+++ b/src/Controller/TaxonomiesController.php
@@ -40,7 +40,7 @@ private function getEditableConfig() {
   /**
    * Function to export taxonomy terms.
    */
-  public function exportTaxonomies(array $form = NULL, FormStateInterface $form_state = NULL) {
+  public function exportTaxonomies(?array $form = NULL, ?FormStateInterface $form_state = NULL) {
     StructureSyncHelper::logMessage('Taxonomies export started');
 
     if (is_object($form_state) && $form_state->hasValue('export_voc_list')) {
@@ -163,7 +163,7 @@ public function exportTaxonomies(array $form = NULL, FormStateInterface $form_st
    * an array with a key value pair for form with key 'style' and value 'full',
    * 'safe' or 'force' to apply that import style.
    */
-  public function importTaxonomies(array $form, FormStateInterface $form_state = NULL) {
+  public function importTaxonomies(array $form, ?FormStateInterface $form_state = NULL) {
     StructureSyncHelper::logMessage('Taxonomy import started');
 
     // Check if the import style has been defined in the form (state) and else
diff --git a/src/StructureSyncHelper.php b/src/StructureSyncHelper.php
index caf2fe2a3eab0abf3801ec8a6da36178620e7e25..cab38c596e0156b5eac7d465abfbf7c3be6dbbbf 100644
--- a/src/StructureSyncHelper.php
+++ b/src/StructureSyncHelper.php
@@ -15,7 +15,7 @@ class StructureSyncHelper {
   /**
    * Function to export taxonomy terms.
    */
-  public static function exportTaxonomies(array $form = NULL, FormStateInterface $form_state = NULL) {
+  public static function exportTaxonomies(?array $form = NULL, ?FormStateInterface $form_state = NULL) {
     $taxonomiesController = new TaxonomiesController();
     $taxonomiesController->exportTaxonomies($form, $form_state);
   }
@@ -23,7 +23,7 @@ public static function exportTaxonomies(array $form = NULL, FormStateInterface $
   /**
    * Function to export custom blocks.
    */
-  public static function exportCustomBlocks(array $form = NULL, FormStateInterface $form_state = NULL) {
+  public static function exportCustomBlocks(?array $form = NULL, ?FormStateInterface $form_state = NULL) {
     $blocksController = new BlocksController();
     $blocksController->exportBlocks($form, $form_state);
   }
@@ -31,7 +31,7 @@ public static function exportCustomBlocks(array $form = NULL, FormStateInterface
   /**
    * Function to export menu links.
    */
-  public static function exportMenuLinks(array $form = NULL, FormStateInterface $form_state = NULL) {
+  public static function exportMenuLinks(?array $form = NULL, ?FormStateInterface $form_state = NULL) {
     $menuLinksController = MenuLinksController::create(\Drupal::getContainer());
     $menuLinksController->exportMenuLinks($form, $form_state);
   }
@@ -43,7 +43,7 @@ public static function exportMenuLinks(array $form = NULL, FormStateInterface $f
    * an array with a key value pair for form with key 'style' and value 'full',
    * 'safe' or 'force' to apply that import style.
    */
-  public static function importTaxonomies(array $form, FormStateInterface $form_state = NULL) {
+  public static function importTaxonomies(array $form, ?FormStateInterface $form_state = NULL) {
     $taxonomiesController = new TaxonomiesController();
     $taxonomiesController->importTaxonomies($form, $form_state);
   }
@@ -55,7 +55,7 @@ public static function importTaxonomies(array $form, FormStateInterface $form_st
    * an array with a key value pair for form with key 'style' and value 'full',
    * 'safe' or 'force' to apply that import style.
    */
-  public static function importCustomBlocks(array $form, FormStateInterface $form_state = NULL) {
+  public static function importCustomBlocks(array $form, ?FormStateInterface $form_state = NULL) {
     $customBlocksController = new BlocksController();
     $customBlocksController->importBlocks($form, $form_state);
   }
@@ -67,7 +67,7 @@ public static function importCustomBlocks(array $form, FormStateInterface $form_
    * an array with a key value pair for form with key 'style' and value 'full',
    * 'safe' or 'force' to apply that import style.
    */
-  public static function importMenuLinks(array $form, FormStateInterface $form_state = NULL) {
+  public static function importMenuLinks(array $form, ?FormStateInterface $form_state = NULL) {
     $menuLinksController = MenuLinksController::create(\Drupal::getContainer());
     $menuLinksController->importMenuLinks($form, $form_state);
   }
@@ -100,7 +100,7 @@ public static function logMessage($message, $type = NULL, $context = []) {
   /**
    * Function to start importing taxonomies with the 'full' style.
    */
-  public static function importTaxonomiesFull(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importTaxonomiesFull(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'full';
 
     StructureSyncHelper::importTaxonomies($form, $form_state);
@@ -109,7 +109,7 @@ public static function importTaxonomiesFull(array &$form, FormStateInterface $fo
   /**
    * Function to start importing taxonomies with the 'safe' style.
    */
-  public static function importTaxonomiesSafe(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importTaxonomiesSafe(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'safe';
 
     StructureSyncHelper::importTaxonomies($form, $form_state);
@@ -118,7 +118,7 @@ public static function importTaxonomiesSafe(array &$form, FormStateInterface $fo
   /**
    * Function to start importing taxonomies with the 'force' style.
    */
-  public static function importTaxonomiesForce(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importTaxonomiesForce(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'force';
 
     StructureSyncHelper::importTaxonomies($form, $form_state);
@@ -127,7 +127,7 @@ public static function importTaxonomiesForce(array &$form, FormStateInterface $f
   /**
    * Function to start importing custom blocks with the 'full' style.
    */
-  public static function importCustomBlocksFull(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importCustomBlocksFull(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'full';
 
     StructureSyncHelper::importCustomBlocks($form, $form_state);
@@ -136,7 +136,7 @@ public static function importCustomBlocksFull(array &$form, FormStateInterface $
   /**
    * Function to start importing custom blocks with the 'safe' style.
    */
-  public static function importCustomBlocksSafe(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importCustomBlocksSafe(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'safe';
 
     StructureSyncHelper::importCustomBlocks($form, $form_state);
@@ -145,7 +145,7 @@ public static function importCustomBlocksSafe(array &$form, FormStateInterface $
   /**
    * Function to start importing custom blocks with the 'force' style.
    */
-  public static function importCustomBlocksForce(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importCustomBlocksForce(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'force';
 
     StructureSyncHelper::importCustomBlocks($form, $form_state);
@@ -154,7 +154,7 @@ public static function importCustomBlocksForce(array &$form, FormStateInterface
   /**
    * Function to start importing menu links with the 'full' style.
    */
-  public static function importMenuLinksFull(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importMenuLinksFull(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'full';
 
     StructureSyncHelper::importMenuLinks($form, $form_state);
@@ -163,7 +163,7 @@ public static function importMenuLinksFull(array &$form, FormStateInterface $for
   /**
    * Function to start importing menu links with the 'safe' style.
    */
-  public static function importMenuLinksSafe(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importMenuLinksSafe(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'safe';
 
     StructureSyncHelper::importMenuLinks($form, $form_state);
@@ -172,7 +172,7 @@ public static function importMenuLinksSafe(array &$form, FormStateInterface $for
   /**
    * Function to start importing menu links with the 'force' style.
    */
-  public static function importMenuLinksForce(array &$form, FormStateInterface $form_state = NULL) {
+  public static function importMenuLinksForce(array &$form, ?FormStateInterface $form_state = NULL) {
     $form['style'] = 'force';
 
     StructureSyncHelper::importMenuLinks($form, $form_state);
diff --git a/structure_sync.info.yml b/structure_sync.info.yml
index 7776f05c121dda6c01308251365bd2fac08d4c5a..c3fb1303665d5ab8b7d0ef7e5152aae7fa5ae90b 100644
--- a/structure_sync.info.yml
+++ b/structure_sync.info.yml
@@ -1,6 +1,6 @@
 name: 'Structure Sync'
 description: 'Tool for syncing structural data that is stored as content.'
-core_version_requirement: ^8 || ^9 || ^10 || ^11
+core_version_requirement: ^10.3 || ^11
 configure: structure_sync.general.form
 dependencies:
   - drupal:taxonomy