diff --git a/CHANGELOG.md b/CHANGELOG.md
index 766400a..09bf2f2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+# Version 23.1.0
+
+## Features
+
+### PHP 8.4 Compatibility
+
+* Add PHP 8.4 support
+
 # Version 23.0.0
 
 ## Features
diff --git a/composer.json b/composer.json
index 8cc590c..d587620 100755
--- a/composer.json
+++ b/composer.json
@@ -4,7 +4,7 @@
     "license": "MIT",
     "require": {
         "php": "^8.1",
-        "techdivision/import": "^18.0.0"
+        "techdivision/import": "^18.1"
     },
     "require-dev": {
         "doctrine/dbal": "^4.0.4",
diff --git a/src/Callbacks/CreateMultiselectOptionValueCallback.php b/src/Callbacks/CreateMultiselectOptionValueCallback.php
index 1ea32a8..a12bdd6 100644
--- a/src/Callbacks/CreateMultiselectOptionValueCallback.php
+++ b/src/Callbacks/CreateMultiselectOptionValueCallback.php
@@ -75,7 +75,7 @@ protected function getUniqueIdentifier()
      *
      * @return mixed The modified value
      */
-    public function handle(AttributeCodeAndValueAwareObserverInterface $observer = null)
+    public function handle(?AttributeCodeAndValueAwareObserverInterface $observer = null)
     {
 
         // set the observer
diff --git a/src/Callbacks/CreateSelectOptionValueCallback.php b/src/Callbacks/CreateSelectOptionValueCallback.php
index 3a6c245..04b3b2b 100644
--- a/src/Callbacks/CreateSelectOptionValueCallback.php
+++ b/src/Callbacks/CreateSelectOptionValueCallback.php
@@ -75,7 +75,7 @@ protected function getUniqueIdentifier()
      *
      * @return mixed The modified value
      */
-    public function handle(AttributeCodeAndValueAwareObserverInterface $observer = null)
+    public function handle(?AttributeCodeAndValueAwareObserverInterface $observer = null)
     {
 
         // set the observer
diff --git a/src/Observers/AttributeOptionObserver.php b/src/Observers/AttributeOptionObserver.php
index 97bf836..366e69e 100644
--- a/src/Observers/AttributeOptionObserver.php
+++ b/src/Observers/AttributeOptionObserver.php
@@ -69,15 +69,15 @@ class AttributeOptionObserver extends AbstractAttributeImportObserver implements
      * Initializes the observer with the passed subject instance.
      *
      * @param \TechDivision\Import\Attribute\Services\AttributeBunchProcessorInterface $attributeBunchProcessor The attribute bunch processor instance
-     * @param \TechDivision\Import\Observers\AttributeLoaderInterface                  $attributeLoader         The attribute loader instance
-     * @param \TechDivision\Import\Observers\EntityMergers\EntityMergerInterface       $entityMerger            The entity merger instance
+     * @param \TechDivision\Import\Observers\AttributeLoaderInterface|null                  $attributeLoader         The attribute loader instance
+     * @param \TechDivision\Import\Observers\EntityMergers\EntityMergerInterface|null       $entityMerger            The entity merger instance
      * @param \TechDivision\Import\Observers\StateDetectorInterface|null               $stateDetector           The state detector instance to use
      */
     public function __construct(
         AttributeBunchProcessorInterface $attributeBunchProcessor,
-        AttributeLoaderInterface $attributeLoader = null,
-        EntityMergerInterface $entityMerger = null,
-        StateDetectorInterface $stateDetector = null
+        ?AttributeLoaderInterface $attributeLoader = null,
+        ?EntityMergerInterface $entityMerger = null,
+        ?StateDetectorInterface $stateDetector = null
     ) {
 
             // initialize the bunch processor, the attribute loader and the entity merger instance
diff --git a/src/Observers/CatalogAttributeObserver.php b/src/Observers/CatalogAttributeObserver.php
index b78ae62..e94a1f3 100644
--- a/src/Observers/CatalogAttributeObserver.php
+++ b/src/Observers/CatalogAttributeObserver.php
@@ -76,15 +76,15 @@ class CatalogAttributeObserver extends AbstractAttributeImportObserver
      * Initializes the observer with the passed subject instance.
      *
      * @param \TechDivision\Import\Attribute\Services\AttributeBunchProcessorInterface $attributeBunchProcessor The attribute bunch processor instance
-     * @param \TechDivision\Import\Observers\EntityMergers\EntityMergerInterface       $entityMerger            The entity merger instance
+     * @param \TechDivision\Import\Observers\EntityMergers\EntityMergerInterface|null       $entityMerger            The entity merger instance
      * @param \TechDivision\Import\Loaders\LoaderInterface|null                        $headerMappingLoader     The loader for the virtual mappings
      * @param \TechDivision\Import\Observers\StateDetectorInterface|null               $stateDetector           The state detector instance to use
      */
     public function __construct(
         AttributeBunchProcessorInterface $attributeBunchProcessor,
-        EntityMergerInterface $entityMerger = null,
-        LoaderInterface $headerMappingLoader = null,
-        StateDetectorInterface $stateDetector = null
+        ?EntityMergerInterface $entityMerger = null,
+        ?LoaderInterface $headerMappingLoader = null,
+        ?StateDetectorInterface $stateDetector = null
     ) {
 
         // initialize the bunch processor and the entity merger instance
diff --git a/src/Observers/EntityAttributeObserver.php b/src/Observers/EntityAttributeObserver.php
index ce00f7c..1b7d867 100644
--- a/src/Observers/EntityAttributeObserver.php
+++ b/src/Observers/EntityAttributeObserver.php
@@ -98,13 +98,13 @@ class EntityAttributeObserver extends AbstractAttributeImportObserver
      * Initializes the observer with the passed subject instance.
      *
      * @param \TechDivision\Import\Attribute\Services\AttributeBunchProcessorInterface $attributeBunchProcessor The attribute bunch processor instance
-     * @param \TechDivision\Import\Observers\EntityMergers\EntityMergerInterface       $entityMerger            The entity merger instance
+     * @param \TechDivision\Import\Observers\EntityMergers\EntityMergerInterface|null       $entityMerger            The entity merger instance
      * @param \TechDivision\Import\Observers\StateDetectorInterface|null               $stateDetector           The state detector instance to use
      */
     public function __construct(
         AttributeBunchProcessorInterface $attributeBunchProcessor,
-        EntityMergerInterface $entityMerger = null,
-        StateDetectorInterface $stateDetector = null
+        ?EntityMergerInterface $entityMerger = null,
+        ?StateDetectorInterface $stateDetector = null
     ) {
 
         // initialize the bunch processor and the entity merger instance