diff --git a/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserText.php b/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserText.php
index c057d38cc5d06b1ab4b7dc4313b23f418ec48a3c..0035ec13766428a81a935bae2f53e0febb32db2d 100644
--- a/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserText.php
+++ b/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserText.php
@@ -23,7 +23,7 @@ class ParagraphsDemoUserText extends ParagraphsConversionBase {
   /**
    * {@inheritdoc}
    */
-  public function convert(array $settings, ParagraphInterface $original_paragraph, array $converted_paragraphs = NULL) {
+  public function convert(array $settings, ParagraphInterface $original_paragraph, ?array $converted_paragraphs = NULL) {
     $username = "Empty user field";
     if ($original_paragraph->get('field_user_demo')->entity) {
       $username = $original_paragraph->get('field_user_demo')->entity->label();
diff --git a/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserToTextUser.php b/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserToTextUser.php
index 533e892948ec3379888abe848638f64a6aec8e77..812a224cb048cafbfeddca7487df92a789502e5d 100644
--- a/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserToTextUser.php
+++ b/modules/paragraphs_demo/src/Plugin/paragraphs/Conversion/ParagraphsDemoUserToTextUser.php
@@ -22,7 +22,7 @@ class ParagraphsDemoUserToTextUser extends ParagraphsConversionBase {
   /**
    * {@inheritdoc}
    */
-  public function convert(array $settings, ParagraphInterface $original_paragraph, array $converted_paragraphs = NULL) {
+  public function convert(array $settings, ParagraphInterface $original_paragraph, ?array $converted_paragraphs = NULL) {
     $username = "Empty user field";
     $user = NULL;
     if ($original_paragraph->get('field_user_demo')->entity) {
diff --git a/modules/paragraphs_type_permissions/paragraphs_type_permissions.module b/modules/paragraphs_type_permissions/paragraphs_type_permissions.module
index e3757416f9b1998f59fd96896aec3f913efcf5f3..216cd2e9cea9369eb674eabb71bc8383b53c60e0 100644
--- a/modules/paragraphs_type_permissions/paragraphs_type_permissions.module
+++ b/modules/paragraphs_type_permissions/paragraphs_type_permissions.module
@@ -69,7 +69,7 @@ function paragraphs_type_permissions_paragraph_access(ParagraphInterface $entity
 /**
  * Implements hook_ENTITY_TYPE_create_access() for entity type "paragraph".
  */
-function paragraphs_type_permissions_paragraph_create_access(AccountInterface $account = NULL, array $context = array(), $entity_bundle = NULL) {
+function paragraphs_type_permissions_paragraph_create_access(?AccountInterface $account = NULL, array $context = array(), $entity_bundle = NULL) {
   $permissions = &drupal_static(__FUNCTION__, array());
 
   // Set static cache id to use the type machine name.
diff --git a/src/ParagraphsConversionBase.php b/src/ParagraphsConversionBase.php
index 890aa2daff79fb2d62836472446b678c96f00a86..45fea15da9b8e380a8dedae53414b3263b2dc6b3 100644
--- a/src/ParagraphsConversionBase.php
+++ b/src/ParagraphsConversionBase.php
@@ -97,14 +97,14 @@ abstract class ParagraphsConversionBase extends PluginBase implements Paragraphs
   /**
    * {@inheritdoc}
    */
-  public function convert(array $settings, ParagraphInterface $original_paragraph, array $converted_paragraph = NULL) {
+  public function convert(array $settings, ParagraphInterface $original_paragraph, ?array $converted_paragraph = NULL) {
     return NULL;
   }
 
   /**
    * {@inheritdoc}
    */
-  public function supports(ParagraphInterface $paragraph, array $parent_allowed_types = NULL) {
+  public function supports(ParagraphInterface $paragraph, ?array $parent_allowed_types = NULL) {
     return $paragraph->getType() == $this->getPluginDefinition()['source_type'];
   }
 
diff --git a/src/ParagraphsConversionInterface.php b/src/ParagraphsConversionInterface.php
index 6fae7fa33d7b442d2de861fce4d5208a24229ed3..cc1954fa6de4b9a62415d052b05efd8ba93a5cd8 100644
--- a/src/ParagraphsConversionInterface.php
+++ b/src/ParagraphsConversionInterface.php
@@ -61,7 +61,7 @@ interface ParagraphsConversionInterface extends PluginFormInterface, Configurabl
    * @param array $converted_paragraphs
    *   (optional) The array of converted paragraphs.
    */
-  public function convert(array $settings, ParagraphInterface $original_paragraph, array $converted_paragraphs = NULL);
+  public function convert(array $settings, ParagraphInterface $original_paragraph, ?array $converted_paragraphs = NULL);
 
   /**
    * Check if the current plugin supports conversion for a paragraph.
@@ -74,6 +74,6 @@ interface ParagraphsConversionInterface extends PluginFormInterface, Configurabl
    * @param array $parent_allowed_types
    *   (optional) The allowed paragraph types on the parent field.
    */
-  public function supports(ParagraphInterface $paragraph, array $parent_allowed_types = NULL);
+  public function supports(ParagraphInterface $paragraph, ?array $parent_allowed_types = NULL);
 
 }
diff --git a/src/ParagraphsConversionManager.php b/src/ParagraphsConversionManager.php
index 2317237119983e17dd4668597d17d8826e333b17..96f55026b630a05553018be584d94abf726701c4 100644
--- a/src/ParagraphsConversionManager.php
+++ b/src/ParagraphsConversionManager.php
@@ -66,7 +66,7 @@ class ParagraphsConversionManager extends DefaultPluginManager {
    * @return array
    *   The applicable conversion plugins.
    */
-  public function getApplicableDefinitions(ParagraphInterface $paragraph, array $allowed_types = NULL) {
+  public function getApplicableDefinitions(ParagraphInterface $paragraph, ?array $allowed_types = NULL) {
     $definitions = $this->getDefinitions();
     $applicable_plugins = [];
     foreach ($definitions as $key => $definition) {
@@ -92,7 +92,7 @@ class ParagraphsConversionManager extends DefaultPluginManager {
    * @return bool
    *   TRUE if the plugin is applicable. Otherwise, FALSE.
    */
-  protected function isApplicable(ParagraphsConversionInterface $plugin, ParagraphInterface $paragraph, array $allowed_types = NULL) {
+  protected function isApplicable(ParagraphsConversionInterface $plugin, ParagraphInterface $paragraph, ?array $allowed_types = NULL) {
     if (!$plugin->supports($paragraph, $allowed_types)) {
       return FALSE;
     }
@@ -135,7 +135,7 @@ class ParagraphsConversionManager extends DefaultPluginManager {
    * @return bool
    *   Whether the current paragraph supports conversion.
    */
-  public function supportsConversion(ParagraphInterface $paragraph, array $allowed_types = NULL) {
+  public function supportsConversion(ParagraphInterface $paragraph, ?array $allowed_types = NULL) {
     $definitions = $this->getDefinitions();
     foreach ($definitions as $key => $definition) {
       /** @var \Drupal\paragraphs\ParagraphsConversionInterface $plugin */
diff --git a/src/Plugin/Field/FieldWidget/ParagraphsWidget.php b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
index 42f823189cbfd64e245efbc30a1c534572d28455..c40afea6667c7080231348ccfaaa0648a8dfa534 100644
--- a/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
+++ b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
@@ -1250,7 +1250,7 @@ class ParagraphsWidget extends WidgetBase {
    *     - label: The label of the paragraph type.
    *     - weight: The weight of the paragraph type.
    */
-  public function getAllowedTypes(FieldDefinitionInterface $field_definition = NULL) {
+  public function getAllowedTypes(?FieldDefinitionInterface $field_definition = NULL) {
 
     $return_bundles = array();
     /** @var \Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManagerInterface $selection_manager */
@@ -1533,7 +1533,7 @@ class ParagraphsWidget extends WidgetBase {
    * @return \Drupal\paragraphs\Entity\Paragraph[]
    *   Child paragraphs.
    */
-  protected function getChildParagraphs(FormStateInterface $form_state, $field_name, ParagraphInterface $paragraph = NULL, array $array_parents = []) {
+  protected function getChildParagraphs(FormStateInterface $form_state, $field_name, ?ParagraphInterface $paragraph = NULL, array $array_parents = []) {
 
     // Convert the parents structure which only includes field names and delta
     // to the full storage array key which includes a prefix and a subform.
@@ -1592,7 +1592,7 @@ class ParagraphsWidget extends WidgetBase {
    * @return array
    *   The built form structure.
    */
-  protected function buildNestedParagraphsFoDragDrop(FormStateInterface $form_state, ParagraphInterface $paragraph = NULL, array $array_parents = []) {
+  protected function buildNestedParagraphsFoDragDrop(FormStateInterface $form_state, ?ParagraphInterface $paragraph = NULL, array $array_parents = []) {
     // Look for nested elements.
     $elements = [];
     $field_definitions = [];
@@ -2349,7 +2349,7 @@ class ParagraphsWidget extends WidgetBase {
       $new_field_storage[$field_name] = $clear_paragraphs($new_field_storage[$field_name]);
     }
 
-    $reorder_paragraphs = function ($reorder_values, $parents = [], FieldableEntityInterface $parent_entity = NULL) use ($complete_field_storage, &$new_field_storage, &$reorder_paragraphs) {
+    $reorder_paragraphs = function ($reorder_values, $parents = [], ?FieldableEntityInterface $parent_entity = NULL) use ($complete_field_storage, &$new_field_storage, &$reorder_paragraphs) {
       foreach ($reorder_values as $field_name => $values) {
         foreach ($values['list'] as $delta => $item_values) {
           $old_keys = array_merge(
diff --git a/src/Plugin/migrate/process/ParagraphsLookup.php b/src/Plugin/migrate/process/ParagraphsLookup.php
index f9474810d8b5498aeb81259eae913478d94d1c41..1dc1852513b596d1ab5f5cd611509094a63b77d8 100644
--- a/src/Plugin/migrate/process/ParagraphsLookup.php
+++ b/src/Plugin/migrate/process/ParagraphsLookup.php
@@ -77,7 +77,7 @@ class ParagraphsLookup extends MigrationLookup {
   /**
    * {@inheritdoc}
    */
-  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, ?MigrationInterface $migration = NULL) {
     return new static(
       $configuration,
       $plugin_id,
diff --git a/tests/modules/paragraphs_test/src/Plugin/paragraphs/Conversion/ParagraphsTestTextToTextImage.php b/tests/modules/paragraphs_test/src/Plugin/paragraphs/Conversion/ParagraphsTestTextToTextImage.php
index cb94712f09e1ad32b37c2a24f52ddf19d8dc08b4..2d48ef6e768003a9cde52c363311c3054503d8d7 100644
--- a/tests/modules/paragraphs_test/src/Plugin/paragraphs/Conversion/ParagraphsTestTextToTextImage.php
+++ b/tests/modules/paragraphs_test/src/Plugin/paragraphs/Conversion/ParagraphsTestTextToTextImage.php
@@ -21,7 +21,7 @@ class ParagraphsTestTextToTextImage extends ParagraphsConversionBase {
   /**
    * {@inheritdoc}
    */
-  public function submitConversion(array $settings, ParagraphInterface $original_paragraph, array $converted_paragraphs = NULL) {
+  public function submitConversion(array $settings, ParagraphInterface $original_paragraph, ?array $converted_paragraphs = NULL) {
     $text = $original_paragraph->get('field_text_demo')->value;
     return [
       [