diff --git a/composer.json b/composer.json
index 4b090f1c..4337c483 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,7 @@
 		"source": "https://github.com/cebe/yii2-openapi"
 	},
 	"require": {
-		"php": ">=7.2.0",
+		"php": "^7.4 || ^8.0",
 		"cebe/php-openapi": "^1.5.0",
 		"yiisoft/yii2": "~2.0.48",
 		"yiisoft/yii2-gii": "~2.0.0 | ~2.1.0 | ~2.2.0| ~2.3.0",
diff --git a/src/generator/default/transformer.php b/src/generator/default/transformer.php
index c118a004..734e1dec 100644
--- a/src/generator/default/transformer.php
+++ b/src/generator/default/transformer.php
@@ -23,14 +23,14 @@
 class <?=$transformer->name?> extends TransformerAbstract
 {
 <?php if (!empty($transformer->availableRelations)):?>
-    protected $availableIncludes = ['<?=implode("', '", $transformer->availableRelations)?>'];
+    protected array $availableIncludes = ['<?=implode("', '", $transformer->availableRelations)?>'];
 <?php else:?>
-    protected $availableIncludes = [];
+    protected array $availableIncludes = [];
 <?php endif;?>
 <?php if (!empty($transformer->defaultRelations)):?>
-    protected $defaultIncludes = ['<?=implode("', '", $transformer->defaultRelations)?>'];
+    protected array $defaultIncludes = ['<?=implode("', '", $transformer->defaultRelations)?>'];
 <?php else:?>
-    protected $defaultIncludes = [];
+    protected array $defaultIncludes = [];
 <?php endif;?>
 
     public function transform(<?=$transformer->dbModel->getClassName()?> $model)
diff --git a/tests/specs/blog_jsonapi/transformers/base/CategoryTransformer.php b/tests/specs/blog_jsonapi/transformers/base/CategoryTransformer.php
index 4abd3bab..0aa97dc5 100644
--- a/tests/specs/blog_jsonapi/transformers/base/CategoryTransformer.php
+++ b/tests/specs/blog_jsonapi/transformers/base/CategoryTransformer.php
@@ -7,8 +7,8 @@
 
 class CategoryTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['posts'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['posts'];
+    protected array $defaultIncludes = [];
 
     public function transform(Category $model)
     {
diff --git a/tests/specs/blog_jsonapi/transformers/base/CommentTransformer.php b/tests/specs/blog_jsonapi/transformers/base/CommentTransformer.php
index 8de529f3..c5a6dae8 100644
--- a/tests/specs/blog_jsonapi/transformers/base/CommentTransformer.php
+++ b/tests/specs/blog_jsonapi/transformers/base/CommentTransformer.php
@@ -8,8 +8,8 @@
 
 class CommentTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['post', 'user'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['post', 'user'];
+    protected array $defaultIncludes = [];
 
     public function transform(Comment $model)
     {
diff --git a/tests/specs/blog_jsonapi/transformers/base/PostTagTransformer.php b/tests/specs/blog_jsonapi/transformers/base/PostTagTransformer.php
index 58c93d3e..004688e7 100644
--- a/tests/specs/blog_jsonapi/transformers/base/PostTagTransformer.php
+++ b/tests/specs/blog_jsonapi/transformers/base/PostTagTransformer.php
@@ -8,8 +8,8 @@
 
 class PostTagTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['post', 'tag'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['post', 'tag'];
+    protected array $defaultIncludes = [];
 
     public function transform(PostTag $model)
     {
diff --git a/tests/specs/blog_jsonapi/transformers/base/PostTransformer.php b/tests/specs/blog_jsonapi/transformers/base/PostTransformer.php
index d58c13c7..a49407bc 100644
--- a/tests/specs/blog_jsonapi/transformers/base/PostTransformer.php
+++ b/tests/specs/blog_jsonapi/transformers/base/PostTransformer.php
@@ -10,8 +10,8 @@
 
 class PostTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['category', 'author', 'comments', 'postTags'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['category', 'author', 'comments', 'postTags'];
+    protected array $defaultIncludes = [];
 
     public function transform(Post $model)
     {
diff --git a/tests/specs/blog_jsonapi/transformers/base/TagTransformer.php b/tests/specs/blog_jsonapi/transformers/base/TagTransformer.php
index 91249ab3..bad38fe8 100644
--- a/tests/specs/blog_jsonapi/transformers/base/TagTransformer.php
+++ b/tests/specs/blog_jsonapi/transformers/base/TagTransformer.php
@@ -7,8 +7,8 @@
 
 class TagTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['postTags'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['postTags'];
+    protected array $defaultIncludes = [];
 
     public function transform(Tag $model)
     {
diff --git a/tests/specs/blog_jsonapi/transformers/base/UserTransformer.php b/tests/specs/blog_jsonapi/transformers/base/UserTransformer.php
index 4e07982d..33593e65 100644
--- a/tests/specs/blog_jsonapi/transformers/base/UserTransformer.php
+++ b/tests/specs/blog_jsonapi/transformers/base/UserTransformer.php
@@ -6,8 +6,8 @@
 
 class UserTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = [];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = [];
+    protected array $defaultIncludes = [];
 
     public function transform(User $model)
     {
diff --git a/tests/specs/many2many/transformers/PhotoTransformer.php b/tests/specs/many2many/transformers/PhotoTransformer.php
index 19633a51..b5f34060 100644
--- a/tests/specs/many2many/transformers/PhotoTransformer.php
+++ b/tests/specs/many2many/transformers/PhotoTransformer.php
@@ -6,8 +6,8 @@
 
 class PhotoTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['postsAttaches', 'postsGallery', 'photosPosts', 'targets', 'articles', 'posts'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['postsAttaches', 'postsGallery', 'photosPosts', 'targets', 'articles', 'posts'];
+    protected array $defaultIncludes = [];
 
     public function transform(Photo $model)
     {
diff --git a/tests/specs/many2many/transformers/Photos2PostsTransformer.php b/tests/specs/many2many/transformers/Photos2PostsTransformer.php
index 49602e42..36871189 100644
--- a/tests/specs/many2many/transformers/Photos2PostsTransformer.php
+++ b/tests/specs/many2many/transformers/Photos2PostsTransformer.php
@@ -6,8 +6,8 @@
 
 class Photos2PostsTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['photo', 'post'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['photo', 'post'];
+    protected array $defaultIncludes = [];
 
     public function transform(Photos2Posts $model)
     {
diff --git a/tests/specs/many2many/transformers/PostTransformer.php b/tests/specs/many2many/transformers/PostTransformer.php
index e492afd4..a06fe739 100644
--- a/tests/specs/many2many/transformers/PostTransformer.php
+++ b/tests/specs/many2many/transformers/PostTransformer.php
@@ -6,8 +6,8 @@
 
 class PostTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['postsAttaches', 'postsGallery', 'postsPhotos', 'tags', 'attaches', 'images', 'photos'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['postsAttaches', 'postsGallery', 'postsPhotos', 'tags', 'attaches', 'images', 'photos'];
+    protected array $defaultIncludes = [];
 
     public function transform(Post $model)
     {
diff --git a/tests/specs/many2many/transformers/PostsAttachesTransformer.php b/tests/specs/many2many/transformers/PostsAttachesTransformer.php
index fbb26bb8..22f88296 100644
--- a/tests/specs/many2many/transformers/PostsAttachesTransformer.php
+++ b/tests/specs/many2many/transformers/PostsAttachesTransformer.php
@@ -6,8 +6,8 @@
 
 class PostsAttachesTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['attach', 'target'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['attach', 'target'];
+    protected array $defaultIncludes = [];
 
     public function transform(PostsAttaches $model)
     {
diff --git a/tests/specs/many2many/transformers/PostsGalleryTransformer.php b/tests/specs/many2many/transformers/PostsGalleryTransformer.php
index 524dd4a3..c0b5df98 100644
--- a/tests/specs/many2many/transformers/PostsGalleryTransformer.php
+++ b/tests/specs/many2many/transformers/PostsGalleryTransformer.php
@@ -6,8 +6,8 @@
 
 class PostsGalleryTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['image', 'article'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['image', 'article'];
+    protected array $defaultIncludes = [];
 
     public function transform(PostsGallery $model)
     {
diff --git a/tests/specs/many2many/transformers/TagTransformer.php b/tests/specs/many2many/transformers/TagTransformer.php
index c66a7b5e..51e412c9 100644
--- a/tests/specs/many2many/transformers/TagTransformer.php
+++ b/tests/specs/many2many/transformers/TagTransformer.php
@@ -6,8 +6,8 @@
 
 class TagTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['posts'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['posts'];
+    protected array $defaultIncludes = [];
 
     public function transform(Tag $model)
     {
diff --git a/tests/specs/petstore_jsonapi/transformers/DoctorTransformer.php b/tests/specs/petstore_jsonapi/transformers/DoctorTransformer.php
index 657c3828..00c62490 100644
--- a/tests/specs/petstore_jsonapi/transformers/DoctorTransformer.php
+++ b/tests/specs/petstore_jsonapi/transformers/DoctorTransformer.php
@@ -6,8 +6,8 @@
 
 class DoctorTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = [];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = [];
+    protected array $defaultIncludes = [];
 
     public function transform(Doctor $model)
     {
diff --git a/tests/specs/petstore_jsonapi/transformers/PetStatisticTransformer.php b/tests/specs/petstore_jsonapi/transformers/PetStatisticTransformer.php
index 3fd7c29c..64974044 100644
--- a/tests/specs/petstore_jsonapi/transformers/PetStatisticTransformer.php
+++ b/tests/specs/petstore_jsonapi/transformers/PetStatisticTransformer.php
@@ -6,8 +6,8 @@
 
 class PetStatisticTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['parentPet', 'favoritePets', 'topDoctors'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['parentPet', 'favoritePets', 'topDoctors'];
+    protected array $defaultIncludes = [];
 
     public function transform(PetStatistic $model)
     {
diff --git a/tests/specs/petstore_jsonapi/transformers/PetTransformer.php b/tests/specs/petstore_jsonapi/transformers/PetTransformer.php
index 6035f2e3..45f7feab 100644
--- a/tests/specs/petstore_jsonapi/transformers/PetTransformer.php
+++ b/tests/specs/petstore_jsonapi/transformers/PetTransformer.php
@@ -6,8 +6,8 @@
 
 class PetTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = ['duplicates', 'doctor'];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = ['duplicates', 'doctor'];
+    protected array $defaultIncludes = [];
 
     public function transform(Pet $model)
     {
diff --git a/tests/specs/ref_noobject/transformers/PersonWatchTransformer.php b/tests/specs/ref_noobject/transformers/PersonWatchTransformer.php
index 0a7850e0..69c34e80 100644
--- a/tests/specs/ref_noobject/transformers/PersonWatchTransformer.php
+++ b/tests/specs/ref_noobject/transformers/PersonWatchTransformer.php
@@ -6,8 +6,8 @@
 
 class PersonWatchTransformer extends TransformerAbstract
 {
-    protected $availableIncludes = [];
-    protected $defaultIncludes = [];
+    protected array $availableIncludes = [];
+    protected array $defaultIncludes = [];
 
     public function transform(PersonWatch $model)
     {