diff --git a/extensions/mentions/extend.php b/extensions/mentions/extend.php
index a85d04dab..a58dc5764 100644
--- a/extensions/mentions/extend.php
+++ b/extensions/mentions/extend.php
@@ -9,16 +9,14 @@
 
 namespace Flarum\Mentions;
 
-use Flarum\Api\Controller;
-use Flarum\Api\Serializer\BasicPostSerializer;
-use Flarum\Api\Serializer\BasicUserSerializer;
-use Flarum\Api\Serializer\CurrentUserSerializer;
-use Flarum\Api\Serializer\GroupSerializer;
-use Flarum\Api\Serializer\PostSerializer;
+use Flarum\Api\Context;
+use Flarum\Api\Endpoint;
+use Flarum\Api\Resource;
+use Flarum\Api\Schema;
 use Flarum\Approval\Event\PostWasApproved;
 use Flarum\Extend;
 use Flarum\Group\Group;
-use Flarum\Mentions\Api\LoadMentionedByRelationship;
+use Flarum\Mentions\Api\PostResourceFields;
 use Flarum\Post\Event\Deleted;
 use Flarum\Post\Event\Hidden;
 use Flarum\Post\Event\Posted;
@@ -27,7 +25,6 @@ use Flarum\Post\Event\Revised;
 use Flarum\Post\Filter\PostSearcher;
 use Flarum\Post\Post;
 use Flarum\Search\Database\DatabaseSearchDriver;
-use Flarum\Tags\Api\Serializer\TagSerializer;
 use Flarum\User\User;
 
 return [
@@ -60,50 +57,43 @@ return [
         ->namespace('flarum-mentions', __DIR__.'/views'),
 
     (new Extend\Notification())
-        ->type(Notification\PostMentionedBlueprint::class, PostSerializer::class, ['alert'])
-        ->type(Notification\UserMentionedBlueprint::class, PostSerializer::class, ['alert'])
-        ->type(Notification\GroupMentionedBlueprint::class, PostSerializer::class, ['alert']),
+        ->type(Notification\PostMentionedBlueprint::class, ['alert'])
+        ->type(Notification\UserMentionedBlueprint::class, ['alert'])
+        ->type(Notification\GroupMentionedBlueprint::class, ['alert']),
 
-    (new Extend\ApiSerializer(BasicPostSerializer::class))
-        ->hasMany('mentionedBy', BasicPostSerializer::class)
-        ->hasMany('mentionsPosts', BasicPostSerializer::class)
-        ->hasMany('mentionsUsers', BasicUserSerializer::class)
-        ->hasMany('mentionsGroups', GroupSerializer::class)
-        ->attribute('mentionedByCount', function (BasicPostSerializer $serializer, Post $post) {
-            // Only if it was eager loaded.
-            return $post->getAttribute('mentioned_by_count') ?? 0;
+    (new Extend\ApiResource(Resource\PostResource::class))
+        ->fields(PostResourceFields::class)
+        ->endpoint([Endpoint\Index::class, Endpoint\Show::class], function (Endpoint\Index|Endpoint\Show $endpoint): Endpoint\Endpoint {
+            return $endpoint->addDefaultInclude(['mentionedBy', 'mentionedBy.user', 'mentionedBy.discussion']);
+        })
+        ->endpoint(Endpoint\Index::class, function (Endpoint\Index $endpoint): Endpoint\Index {
+            return $endpoint->eagerLoad(['mentionsUsers', 'mentionsPosts', 'mentionsPosts.user', 'mentionsPosts.discussion', 'mentionsGroups']);
         }),
 
-    (new Extend\ApiController(Controller\ShowDiscussionController::class))
-        ->addInclude(['posts.mentionedBy', 'posts.mentionedBy.user', 'posts.mentionedBy.discussion'])
-        ->load([
-            'posts.mentionsUsers', 'posts.mentionsPosts', 'posts.mentionsPosts.user',
-            'posts.mentionsPosts.discussion', 'posts.mentionsGroups'
-        ])
-        ->loadWhere('posts.mentionedBy', LoadMentionedByRelationship::mutateRelation(...))
-        ->prepareDataForSerialization(LoadMentionedByRelationship::countRelation(...)),
+    (new Extend\ApiResource(Resource\DiscussionResource::class))
+        ->endpoint(Endpoint\Index::class, function (Endpoint\Index $endpoint): Endpoint\Index {
+            return $endpoint->eagerLoad([
+                'firstPost.mentionsUsers', 'firstPost.mentionsPosts',
+                'firstPost.mentionsPosts.user', 'firstPost.mentionsPosts.discussion', 'firstPost.mentionsGroups',
+                'lastPost.mentionsUsers', 'lastPost.mentionsPosts',
+                'lastPost.mentionsPosts.user', 'lastPost.mentionsPosts.discussion', 'lastPost.mentionsGroups',
+            ]);
+        })
+        ->endpoint(Endpoint\Show::class, function (Endpoint\Show $endpoint): Endpoint\Show {
+            return $endpoint->addDefaultInclude(['posts.mentionedBy', 'posts.mentionedBy.user', 'posts.mentionedBy.discussion'])
+                ->eagerLoad([
+                    'posts.mentionsUsers', 'posts.mentionsPosts', 'posts.mentionsPosts.user',
+                    'posts.mentionsPosts.discussion', 'posts.mentionsGroups'
+                ]);
+        }),
 
-    (new Extend\ApiController(Controller\ListDiscussionsController::class))
-        ->load([
-            'firstPost.mentionsUsers', 'firstPost.mentionsPosts',
-            'firstPost.mentionsPosts.user', 'firstPost.mentionsPosts.discussion', 'firstPost.mentionsGroups',
-            'lastPost.mentionsUsers', 'lastPost.mentionsPosts',
-            'lastPost.mentionsPosts.user', 'lastPost.mentionsPosts.discussion', 'lastPost.mentionsGroups',
+    (new Extend\ApiResource(Resource\UserResource::class))
+        ->fields(fn () => [
+            Schema\Boolean::make('canMentionGroups')
+                ->visible(fn (User $user, Context $context) => $context->getActor()->id === $user->id)
+                ->get(fn (User $user) => $user->can('mentionGroups')),
         ]),
 
-    (new Extend\ApiController(Controller\ShowPostController::class))
-        ->addInclude(['mentionedBy', 'mentionedBy.user', 'mentionedBy.discussion'])
-        // We wouldn't normally need to eager load on a single model,
-        // but we do so here for visibility scoping.
-        ->loadWhere('mentionedBy', LoadMentionedByRelationship::mutateRelation(...))
-        ->prepareDataForSerialization(LoadMentionedByRelationship::countRelation(...)),
-
-    (new Extend\ApiController(Controller\ListPostsController::class))
-        ->addInclude(['mentionedBy', 'mentionedBy.user', 'mentionedBy.discussion'])
-        ->load(['mentionsUsers', 'mentionsPosts', 'mentionsPosts.user', 'mentionsPosts.discussion', 'mentionsGroups'])
-        ->loadWhere('mentionedBy', LoadMentionedByRelationship::mutateRelation(...))
-        ->prepareDataForSerialization(LoadMentionedByRelationship::countRelation(...)),
-
     (new Extend\Settings)
         ->serializeToForum('allowUsernameMentionFormat', 'flarum-mentions.allow_username_format', 'boolval'),
 
@@ -119,11 +109,6 @@ return [
         ->addFilter(PostSearcher::class, Filter\MentionedFilter::class)
         ->addFilter(PostSearcher::class, Filter\MentionedPostFilter::class),
 
-    (new Extend\ApiSerializer(CurrentUserSerializer::class))
-        ->attribute('canMentionGroups', function (CurrentUserSerializer $serializer, User $user): bool {
-            return $user->can('mentionGroups');
-        }),
-
     // Tag mentions
     (new Extend\Conditional())
         ->whenExtensionEnabled('flarum-tags', fn () => [
@@ -131,18 +116,23 @@ return [
                 ->render(Formatter\FormatTagMentions::class)
                 ->unparse(Formatter\UnparseTagMentions::class),
 
-            (new Extend\ApiSerializer(BasicPostSerializer::class))
-                ->hasMany('mentionsTags', TagSerializer::class),
-
-            (new Extend\ApiController(Controller\ShowDiscussionController::class))
-                ->load(['posts.mentionsTags']),
-
-            (new Extend\ApiController(Controller\ListDiscussionsController::class))
-                ->load([
-                    'firstPost.mentionsTags', 'lastPost.mentionsTags',
+            (new Extend\ApiResource(Resource\PostResource::class))
+                ->fields(fn () => [
+                    Schema\Relationship\ToMany::make('mentionsTags')
+                        ->type('tags'),
                 ]),
 
-            (new Extend\ApiController(Controller\ListPostsController::class))
-                ->load(['mentionsTags']),
+            (new Extend\ApiResource(Resource\DiscussionResource::class))
+                ->endpoint(Endpoint\Show::class, function (Endpoint\Show $endpoint): Endpoint\Show {
+                    return $endpoint->eagerLoad(['posts.mentionsTags']);
+                })
+                ->endpoint(Endpoint\Index::class, function (Endpoint\Index $endpoint): Endpoint\Index {
+                    return $endpoint->eagerLoad(['firstPost.mentionsTags', 'lastPost.mentionsTags']);
+                }),
+
+            (new Extend\ApiResource(Resource\PostResource::class))
+                ->endpoint([Endpoint\Index::class, Endpoint\Show::class], function (Endpoint\Index|Endpoint\Show $endpoint): Endpoint\Endpoint {
+                    return $endpoint->eagerLoad(['mentionsTags']);
+                }),
         ]),
 ];
diff --git a/extensions/mentions/src/Api/LoadMentionedByRelationship.php b/extensions/mentions/src/Api/LoadMentionedByRelationship.php
deleted file mode 100644
index 47bceafb7..000000000
--- a/extensions/mentions/src/Api/LoadMentionedByRelationship.php
+++ /dev/null
@@ -1,82 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Mentions\Api;
-
-use Flarum\Api\Controller\AbstractSerializeController;
-use Flarum\Discussion\Discussion;
-use Flarum\Http\RequestUtil;
-use Flarum\Post\Post;
-use Illuminate\Database\Eloquent\Collection;
-use Illuminate\Database\Eloquent\Relations\BelongsToMany;
-use Psr\Http\Message\ServerRequestInterface;
-
-/**
- * Apply visibility permissions to API data's mentionedBy relationship.
- * And limit mentionedBy to 3 posts only for performance reasons.
- */
-class LoadMentionedByRelationship
-{
-    public static int $maxMentionedBy = 4;
-
-    public static function mutateRelation(BelongsToMany $query, ServerRequestInterface $request): void
-    {
-        $actor = RequestUtil::getActor($request);
-
-        $query
-            ->with(['mentionsPosts', 'mentionsPosts.user', 'mentionsPosts.discussion', 'mentionsUsers'])
-            ->whereVisibleTo($actor)
-            ->oldest()
-            // Limiting a relationship results is only possible because
-            // the Post model uses the \Staudenmeir\EloquentEagerLimit\HasEagerLimit
-            // trait.
-            ->limit(self::$maxMentionedBy);
-    }
-
-    /**
-     * Called using the @see ApiController::prepareDataForSerialization extender.
-     */
-    public static function countRelation(AbstractSerializeController $controller, mixed $data, ServerRequestInterface $request): array
-    {
-        $actor = RequestUtil::getActor($request);
-        $loadable = null;
-
-        if ($data instanceof Discussion) {
-            // We do this because the ShowDiscussionController manipulates the posts
-            // in a way that some of them are just ids.
-            $loadable = $data->posts->filter(function ($post) {
-                return $post instanceof Post;
-            });
-
-            // firstPost and lastPost might have been included in the API response,
-            // so we have to make sure counts are also loaded for them.
-            if ($data->firstPost) {
-                $loadable->push($data->firstPost);
-            }
-
-            if ($data->lastPost) {
-                $loadable->push($data->lastPost);
-            }
-        } elseif ($data instanceof Collection) {
-            $loadable = $data;
-        } elseif ($data instanceof Post) {
-            $loadable = $data->newCollection([$data]);
-        }
-
-        if ($loadable) {
-            $loadable->loadCount([
-                'mentionedBy' => function ($query) use ($actor) {
-                    return $query->whereVisibleTo($actor);
-                }
-            ]);
-        }
-
-        return [];
-    }
-}
diff --git a/extensions/mentions/src/Api/PostResourceFields.php b/extensions/mentions/src/Api/PostResourceFields.php
new file mode 100644
index 000000000..be188e2e0
--- /dev/null
+++ b/extensions/mentions/src/Api/PostResourceFields.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Flarum\Mentions\Api;
+
+use Flarum\Api\Context;
+use Flarum\Api\Schema;
+use Flarum\Post\Post;
+
+class PostResourceFields
+{
+    public static int $maxMentionedBy = 4;
+
+    public function __invoke(): array
+    {
+        return [
+            Schema\Integer::make('mentionedByCount')
+                ->countRelation('mentionedBy'),
+
+            Schema\Relationship\ToMany::make('mentionedBy')
+                ->type('posts')
+                ->includable()
+                ->limit(static::$maxMentionedBy),
+            Schema\Relationship\ToMany::make('mentionsPosts')
+                ->type('posts'),
+            Schema\Relationship\ToMany::make('mentionsUsers')
+                ->type('users'),
+            Schema\Relationship\ToMany::make('mentionsGroups')
+                ->type('groups'),
+        ];
+    }
+}
diff --git a/extensions/mentions/tests/integration/api/ListPostsTest.php b/extensions/mentions/tests/integration/api/ListPostsTest.php
index ab0964648..1e7c22b65 100644
--- a/extensions/mentions/tests/integration/api/ListPostsTest.php
+++ b/extensions/mentions/tests/integration/api/ListPostsTest.php
@@ -11,6 +11,7 @@ namespace Flarum\Mentions\Tests\integration\api\discussions;
 
 use Carbon\Carbon;
 use Flarum\Mentions\Api\LoadMentionedByRelationship;
+use Flarum\Mentions\Api\PostResourceFields;
 use Flarum\Testing\integration\RetrievesAuthorizedUsers;
 use Flarum\Testing\integration\TestCase;
 use Illuminate\Support\Arr;
@@ -167,7 +168,7 @@ class ListPostsTest extends TestCase
         $mentionedBy = $data['relationships']['mentionedBy']['data'];
 
         // Only displays a limited amount of mentioned by posts
-        $this->assertCount(LoadMentionedByRelationship::$maxMentionedBy, $mentionedBy);
+        $this->assertCount(PostResourceFields::$maxMentionedBy, $mentionedBy);
         // Of the limited amount of mentioned by posts, they must be visible to the actor
         $this->assertEquals([102, 104, 105, 106], Arr::pluck($mentionedBy, 'id'));
     }
@@ -187,14 +188,14 @@ class ListPostsTest extends TestCase
             ])
         );
 
-        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $data = json_decode($body = $response->getBody()->getContents(), true)['data'] ?? [];
 
-        $this->assertEquals(200, $response->getStatusCode());
+        $this->assertEquals(200, $response->getStatusCode(), $body);
 
         $mentionedBy = $data[0]['relationships']['mentionedBy']['data'];
 
         // Only displays a limited amount of mentioned by posts
-        $this->assertCount(LoadMentionedByRelationship::$maxMentionedBy, $mentionedBy);
+        $this->assertCount(PostResourceFields::$maxMentionedBy, $mentionedBy);
         // Of the limited amount of mentioned by posts, they must be visible to the actor
         $this->assertEquals([102, 104, 105, 106], Arr::pluck($mentionedBy, 'id'));
     }
@@ -203,7 +204,7 @@ class ListPostsTest extends TestCase
      * @dataProvider mentionedByIncludeProvider
      * @test
      */
-    public function mentioned_by_relation_returns_limited_results_and_shows_only_visible_posts_in_show_discussion_endpoint(string $include)
+    public function mentioned_by_relation_returns_limited_results_and_shows_only_visible_posts_in_show_discussion_endpoint(?string $include)
     {
         $this->prepareMentionedByData();
 
@@ -216,15 +217,18 @@ class ListPostsTest extends TestCase
             ])
         );
 
-        $included = json_decode($response->getBody()->getContents(), true)['included'];
+        $included = json_decode($body = $response->getBody()->getContents(), true)['included'] ?? [];
+
+        $this->assertEquals(200, $response->getStatusCode(), $body);
 
         $mentionedBy = collect($included)
             ->where('type', 'posts')
             ->where('id', 101)
-            ->first()['relationships']['mentionedBy']['data'];
+            ->first()['relationships']['mentionedBy']['data'] ?? null;
 
+        $this->assertNotNull($mentionedBy, 'Mentioned by relation not included');
         // Only displays a limited amount of mentioned by posts
-        $this->assertCount(LoadMentionedByRelationship::$maxMentionedBy, $mentionedBy);
+        $this->assertCount(PostResourceFields::$maxMentionedBy, $mentionedBy);
         // Of the limited amount of mentioned by posts, they must be visible to the actor
         $this->assertEquals([102, 104, 105, 106], Arr::pluck($mentionedBy, 'id'));
     }
@@ -234,7 +238,7 @@ class ListPostsTest extends TestCase
         return [
             ['posts,posts.mentionedBy'],
             ['posts.mentionedBy'],
-            [''],
+            [null],
         ];
     }
 
@@ -250,10 +254,54 @@ class ListPostsTest extends TestCase
             ])
         );
 
-        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $data = json_decode($body = $response->getBody()->getContents(), true)['data'] ?? [];
 
-        $this->assertEquals(200, $response->getStatusCode());
+        $this->assertEquals(200, $response->getStatusCode(), $body);
 
         $this->assertEquals(0, $data['attributes']['mentionedByCount']);
     }
+
+    /** @test */
+    public function mentioned_by_count_works_on_show_endpoint()
+    {
+        $this->prepareMentionedByData();
+
+        // List posts endpoint
+        $response = $this->send(
+            $this->request('GET', '/api/posts/101', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $data = json_decode($body = $response->getBody()->getContents(), true)['data'] ?? [];
+
+        $this->assertEquals(200, $response->getStatusCode(), $body);
+
+        $this->assertEquals(10, $data['attributes']['mentionedByCount']);
+    }
+
+    /** @test */
+    public function mentioned_by_count_works_on_list_endpoint()
+    {
+        $this->prepareMentionedByData();
+
+        // List posts endpoint
+        $response = $this->send(
+            $this->request('GET', '/api/posts', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['discussion' => 100],
+            ])
+        );
+
+        $data = json_decode($body = $response->getBody()->getContents(), true)['data'] ?? [];
+
+        $this->assertEquals(200, $response->getStatusCode(), $body);
+
+        $post101 = collect($data)->where('id', 101)->first();
+        $post112 = collect($data)->where('id', 112)->first();
+
+        $this->assertEquals(10, $post101['attributes']['mentionedByCount']);
+        $this->assertEquals(0, $post112['attributes']['mentionedByCount']);
+    }
 }
diff --git a/framework/core/src/Api/Resource/AbstractDatabaseResource.php b/framework/core/src/Api/Resource/AbstractDatabaseResource.php
index d1265656c..b1429967c 100644
--- a/framework/core/src/Api/Resource/AbstractDatabaseResource.php
+++ b/framework/core/src/Api/Resource/AbstractDatabaseResource.php
@@ -14,7 +14,6 @@ use Flarum\Api\Resource\Concerns\Bootable;
 use Flarum\Api\Resource\Concerns\Extendable;
 use Flarum\Foundation\DispatchEventsTrait;
 use Flarum\User\User;
-use Illuminate\Support\Arr;
 use RuntimeException;
 use Tobyz\JsonApiServer\Context;
 use Tobyz\JsonApiServer\Laravel\EloquentResource as BaseResource;
diff --git a/framework/core/src/Api/Schema/Number.php b/framework/core/src/Api/Schema/Number.php
index 8ae0c0eae..396c32477 100644
--- a/framework/core/src/Api/Schema/Number.php
+++ b/framework/core/src/Api/Schema/Number.php
@@ -2,8 +2,13 @@
 
 namespace Flarum\Api\Schema;
 
-class Number extends Attribute
+use Tobyz\JsonApiServer\Schema\Concerns\GetsRelationAggregates;
+use Tobyz\JsonApiServer\Schema\Contracts\RelationAggregator;
+
+class Number extends Attribute implements RelationAggregator
 {
+    use GetsRelationAggregates;
+
     public static function make(string $name): static
     {
         return (new static($name))
diff --git a/framework/core/src/Extend/ApiResource.php b/framework/core/src/Extend/ApiResource.php
index 47588d30a..0f40d3b80 100644
--- a/framework/core/src/Extend/ApiResource.php
+++ b/framework/core/src/Extend/ApiResource.php
@@ -71,7 +71,7 @@ class ApiResource implements ExtenderInterface
     public function endpoint(string|array $endpointClass, callable|string $mutator): self
     {
         foreach ((array) $endpointClass as $endpointClassItem) {
-            $this->endpoint[$endpointClassItem] = $mutator;
+            $this->endpoint[$endpointClassItem][] = $mutator;
         }
 
         return $this;
@@ -111,7 +111,7 @@ class ApiResource implements ExtenderInterface
     public function field(string|array $field, callable|string $mutator): self
     {
         foreach ((array) $field as $fieldItem) {
-            $this->field[$fieldItem] = $mutator;
+            $this->field[$fieldItem][] = $mutator;
         }
 
         return $this;
@@ -151,7 +151,7 @@ class ApiResource implements ExtenderInterface
     public function sort(string|array $sort, callable|string $mutator): self
     {
         foreach ((array) $sort as $sortItem) {
-            $this->sort[$sortItem] = $mutator;
+            $this->sort[$sortItem][] = $mutator;
         }
 
         return $this;
@@ -189,12 +189,14 @@ class ApiResource implements ExtenderInterface
             foreach ($endpoints as $key => $endpoint) {
                 $endpointClass = $endpoint::class;
 
-                if (isset($this->endpoint[$endpointClass])) {
-                    $mutateEndpoint = ContainerUtil::wrapCallback($this->endpoint[$endpointClass], $container);
-                    $endpoint = $mutateEndpoint($endpoint, $resource);
+                if (! empty($this->endpoint[$endpointClass])) {
+                    foreach ($this->endpoint[$endpointClass] as $mutator) {
+                        $mutateEndpoint = ContainerUtil::wrapCallback($mutator, $container);
+                        $endpoint = $mutateEndpoint($endpoint, $resource);
 
-                    if (! $endpoint instanceof Endpoint) {
-                        throw new \RuntimeException('The endpoint mutator must return an instance of ' . Endpoint::class);
+                        if (! $endpoint instanceof Endpoint) {
+                            throw new \RuntimeException('The endpoint mutator must return an instance of ' . Endpoint::class);
+                        }
                     }
                 }
 
@@ -219,12 +221,14 @@ class ApiResource implements ExtenderInterface
             }
 
             foreach ($fields as $key => $field) {
-                if (isset($this->field[$field->name])) {
-                    $mutateField = ContainerUtil::wrapCallback($this->field[$field->name], $container);
-                    $field = $mutateField($field);
+                if (! empty($this->field[$field->name])) {
+                    foreach ($this->field[$field->name] as $mutator) {
+                        $mutateField = ContainerUtil::wrapCallback($mutator, $container);
+                        $field = $mutateField($field);
 
-                    if (! $field instanceof Field) {
-                        throw new \RuntimeException('The field mutator must return an instance of ' . Field::class);
+                        if (! $field instanceof Field) {
+                            throw new \RuntimeException('The field mutator must return an instance of ' . Field::class);
+                        }
                     }
                 }
 
@@ -249,12 +253,14 @@ class ApiResource implements ExtenderInterface
             }
 
             foreach ($sorts as $key => $sort) {
-                if (isset($this->sort[$sort->name])) {
-                    $mutateSort = ContainerUtil::wrapCallback($this->sort[$sort], $container);
-                    $sort = $mutateSort($sort);
+                if (! empty($this->sort[$sort->name])) {
+                    foreach ($this->sort[$sort->name] as $mutator) {
+                        $mutateSort = ContainerUtil::wrapCallback($mutator, $container);
+                        $sort = $mutateSort($sort);
 
-                    if (! $sort instanceof Sort) {
-                        throw new \RuntimeException('The sort mutator must return an instance of ' . Sort::class);
+                        if (! $sort instanceof Sort) {
+                            throw new \RuntimeException('The sort mutator must return an instance of ' . Sort::class);
+                        }
                     }
                 }