diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7ce9cb96450..cdaebd63f18 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@
 * OpenAPI: Fix error when schema is empty (#4051)
 * OpenAPI: Do not set scheme to oauth2 when generating securitySchemes (#4073)
 * OpenAPI: Fix missing `$ref` when no `type` is used in context (#4076)
+* GraphQL: Fix "Resource class cannot be determined." error when a null iterable field is returned (#4092)
 
 ## 2.6.2
 
diff --git a/features/graphql/query.feature b/features/graphql/query.feature
index 149d39eaef1..fc8441da537 100644
--- a/features/graphql/query.feature
+++ b/features/graphql/query.feature
@@ -59,6 +59,23 @@ Feature: GraphQL query support
     And the JSON node "data.dummy.jsonData.bar" should be equal to 5
     And the JSON node "data.dummy.arrayData[2]" should be equal to baz
 
+  Scenario: Retrieve an item with an iterable null field
+    Given there are 2 dummy with null JSON objects
+    When I send the following GraphQL request:
+    """
+    {
+      withJsonDummy(id: "/with_json_dummies/2") {
+        id
+        json
+      }
+    }
+    """
+    Then the response status code should be 200
+    And the response should be in JSON
+    And the header "Content-Type" should be equal to "application/json"
+    And the JSON node "data.withJsonDummy.id" should be equal to "/with_json_dummies/2"
+    And the JSON node "data.withJsonDummy.json" should be null
+
   Scenario: Retrieve an item through a GraphQL query with variables
     When I have the following GraphQL request:
     """
diff --git a/src/GraphQl/Resolver/Factory/ItemResolverFactory.php b/src/GraphQl/Resolver/Factory/ItemResolverFactory.php
index 1b257b94f69..353834b397b 100644
--- a/src/GraphQl/Resolver/Factory/ItemResolverFactory.php
+++ b/src/GraphQl/Resolver/Factory/ItemResolverFactory.php
@@ -59,7 +59,7 @@ public function __invoke(?string $resourceClass = null, ?string $rootClass = nul
     {
         return function (?array $source, array $args, $context, ResolveInfo $info) use ($resourceClass, $rootClass, $operationName) {
             // Data already fetched and normalized (field or nested resource)
-            if (isset($source[$info->fieldName])) {
+            if ($source && array_key_exists($info->fieldName, $source)) {
                 return $source[$info->fieldName];
             }
 
diff --git a/tests/Behat/DoctrineContext.php b/tests/Behat/DoctrineContext.php
index a62255ed6b5..bbbc943c763 100644
--- a/tests/Behat/DoctrineContext.php
+++ b/tests/Behat/DoctrineContext.php
@@ -80,6 +80,7 @@
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Document\ThirdLevel as ThirdLevelDocument;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Document\UrlEncodedId as UrlEncodedIdDocument;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Document\User as UserDocument;
+use ApiPlatform\Core\Tests\Fixtures\TestBundle\Document\WithJsonDummy as WithJsonDummyDocument;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\AbsoluteUrlDummy;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\AbsoluteUrlRelationDummy;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\Address;
@@ -154,6 +155,7 @@
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\UrlEncodedId;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\User;
 use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\UuidIdentifierDummy;
+use ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity\WithJsonDummy;
 use Behat\Behat\Context\Context;
 use Behat\Gherkin\Node\PyStringNode;
 use Doctrine\ODM\MongoDB\DocumentManager;
@@ -573,6 +575,21 @@ public function thereAreDummyObjectsWithJsonData(int $nb)
         $this->manager->flush();
     }
 
+    /**
+     * @Given there are :nb dummy with null JSON objects
+     */
+    public function thereAreDummyWithNullJsonObjects(int $nb)
+    {
+        for ($i = 1; $i <= $nb; ++$i) {
+            $dummy = $this->buildWithJsonDummy();
+            $dummy->json = null;
+
+            $this->manager->persist($dummy);
+        }
+
+        $this->manager->flush();
+    }
+
     /**
      * @Given there are :nb dummy objects with relatedDummy and its thirdLevel
      * @Given there is :nb dummy object with relatedDummy and its thirdLevel
@@ -2190,4 +2207,12 @@ private function buildCustomMultipleIdentifierDummy()
     {
         return $this->isOrm() ? new CustomMultipleIdentifierDummy() : new CustomMultipleIdentifierDummyDocument();
     }
+
+    /**
+     * @return WithJsonDummy|WithJsonDummyDocument
+     */
+    private function buildWithJsonDummy()
+    {
+        return $this->isOrm() ? new WithJsonDummy() : new WithJsonDummyDocument();
+    }
 }
diff --git a/tests/Fixtures/TestBundle/Document/WithJsonDummy.php b/tests/Fixtures/TestBundle/Document/WithJsonDummy.php
new file mode 100644
index 00000000000..5c33e4ee42c
--- /dev/null
+++ b/tests/Fixtures/TestBundle/Document/WithJsonDummy.php
@@ -0,0 +1,43 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Core\Tests\Fixtures\TestBundle\Document;
+
+use ApiPlatform\Core\Annotation\ApiResource;
+use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;
+
+/**
+ * @ApiResource
+ * @ODM\Document
+ */
+class WithJsonDummy
+{
+    /**
+     * @var int
+     *
+     * @ODM\Id(strategy="INCREMENT", type="int", nullable=true)
+     */
+    private $id;
+
+    /**
+     * @var ?array
+     *
+     * @ODM\Field(type="hash", nullable=true)
+     */
+    public $json;
+
+    public function getId(): int
+    {
+        return $this->id;
+    }
+}
diff --git a/tests/Fixtures/TestBundle/Entity/WithJsonDummy.php b/tests/Fixtures/TestBundle/Entity/WithJsonDummy.php
new file mode 100644
index 00000000000..b3998f858b7
--- /dev/null
+++ b/tests/Fixtures/TestBundle/Entity/WithJsonDummy.php
@@ -0,0 +1,45 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Core\Tests\Fixtures\TestBundle\Entity;
+
+use ApiPlatform\Core\Annotation\ApiResource;
+use Doctrine\ORM\Mapping as ORM;
+
+/**
+ * @ApiResource
+ * @ORM\Entity
+ */
+class WithJsonDummy
+{
+    /**
+     * @var int
+     *
+     * @ORM\Column(type="integer", nullable=true)
+     * @ORM\Id
+     * @ORM\GeneratedValue(strategy="AUTO")
+     */
+    private $id;
+
+    /**
+     * @var ?array
+     *
+     * @ORM\Column(type="json", nullable=true)
+     */
+    public $json;
+
+    public function getId(): int
+    {
+        return $this->id;
+    }
+}
diff --git a/tests/GraphQl/Resolver/Factory/ItemResolverFactoryTest.php b/tests/GraphQl/Resolver/Factory/ItemResolverFactoryTest.php
index 69cc1b31576..06d2c66f627 100644
--- a/tests/GraphQl/Resolver/Factory/ItemResolverFactoryTest.php
+++ b/tests/GraphQl/Resolver/Factory/ItemResolverFactoryTest.php
@@ -118,6 +118,15 @@ public function testResolveNested(): void
         $this->assertSame(['already_serialized'], ($this->itemResolverFactory)('resourceClass')($source, [], null, $info));
     }
 
+    public function testResolveNestedNullValue(): void
+    {
+        $source = ['nestedNullValue' => null];
+        $info = $this->prophesize(ResolveInfo::class)->reveal();
+        $info->fieldName = 'nestedNullValue';
+
+        $this->assertNull(($this->itemResolverFactory)('resourceClass')($source, [], null, $info));
+    }
+
     public function testResolveBadReadStageItem(): void
     {
         $resourceClass = 'stdClass';