diff --git a/src/Bundle/ChillDocGeneratorBundle/Test/DocGenNormalizerTestAbstract.php b/src/Bundle/ChillDocGeneratorBundle/Test/DocGenNormalizerTestAbstract.php
new file mode 100644
index 000000000..2839be3f5
--- /dev/null
+++ b/src/Bundle/ChillDocGeneratorBundle/Test/DocGenNormalizerTestAbstract.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Chill\DocGeneratorBundle\Test;
+
+use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
+use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;
+use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
+
+/**
+ * @template T of object
+ */
+abstract class DocGenNormalizerTestAbstract extends KernelTestCase
+{
+    public function testNullValueHasSameKeysAsNull(): void
+    {
+        $normalizedObject = $this->getNormalizer()->normalize($this->provideNotNullObject(), 'docgen', [
+            AbstractNormalizer::GROUPS => ['docgen:read'], 'docgen:expects' => $this->provideDocGenExpectClass(),
+        ]);
+        $nullNormalizedObject = $this->getNormalizer()->normalize(null, 'docgen', [
+            AbstractNormalizer::GROUPS => ['docgen:read'], 'docgen:expects' => $this->provideDocGenExpectClass(),
+        ]);
+
+        self::assertEqualsCanonicalizing(array_keys($normalizedObject), array_keys($nullNormalizedObject));
+        self::assertArrayHasKey('isNull', $nullNormalizedObject, 'each object must have an "isNull" key');
+        self::assertTrue($nullNormalizedObject['isNull'], 'isNull key must be true for null objects');
+        self::assertFalse($normalizedObject['isNull'], 'isNull key must be false for null objects');
+
+        foreach ($normalizedObject as $key => $value) {
+            if (in_array($key, ['isNull', 'type'])) {
+                continue;
+            }
+
+            if (is_array($value)) {
+                if (array_is_list($value)) {
+                    self::assertEquals([], $nullNormalizedObject[$key], "list must be serialized as an empty array, in {$key}");
+                } else {
+                    self::assertEqualsCanonicalizing(array_keys($value), array_keys($nullNormalizedObject[$key]), "sub-object must have the same keys, in {$key}");
+                }
+            } elseif (is_string($value)) {
+                self::assertEquals('', $nullNormalizedObject[$key], 'strings must be ');
+            }
+        }
+    }
+
+    /**
+     * @return T
+     */
+    abstract public function provideNotNullObject(): object;
+
+    /**
+     * @return class-string<T>
+     */
+    abstract public function provideDocGenExpectClass(): string;
+
+    abstract public function getNormalizer(): NormalizerInterface;
+}