diff --git a/UPGRADE-3.x.md b/UPGRADE-3.x.md
index c16d6ce2..52ef9f1f 100644
--- a/UPGRADE-3.x.md
+++ b/UPGRADE-3.x.md
@@ -4,6 +4,12 @@ UPGRADE 3.x
 UPGRADE FROM 3.x to 3.x
 =======================
 
+### Sonata\DoctrineMongoDBAdminBundle\Model\ModelManager
+
+Deprecated passing `null` as argument 2 for `find()`.
+Deprecated passing `null` or an object which is in state new or removed as argument 1 for `getNormalizedIdentifier()`.
+Deprecated passing `null` as argument 1 for `getUrlSafeIdentifier()`.
+
 UPGRADE FROM 3.3 to 3.4
 =======================
 
diff --git a/src/Model/ModelManager.php b/src/Model/ModelManager.php
index 1c87f0a1..d0258bef 100755
--- a/src/Model/ModelManager.php
+++ b/src/Model/ModelManager.php
@@ -165,7 +165,13 @@ public function delete($object)
 
     public function find($class, $id)
     {
-        if (!isset($id)) {
+        if (null === $id) {
+            @trigger_error(sprintf(
+                'Passing null as argument 1 for %s() is deprecated since'
+                .' sonata-project/doctrine-mongodb-admin-bundle 3.x and will be not allowed in version 4.0.',
+                __METHOD__
+            ), E_USER_DEPRECATED);
+
             return null;
         }
 
@@ -293,7 +299,14 @@ public function getIdentifierFieldNames($class)
 
     public function getNormalizedIdentifier($document)
     {
+        // NEXT_MAJOR: Remove the following 2 checks and declare "object" as type for argument 1.
         if (null === $document) {
+            @trigger_error(sprintf(
+                'Passing null as argument 1 for %s() is deprecated since'
+                .' sonata-project/doctrine-mongodb-admin-bundle 3.x and will be not allowed in version 4.0.',
+                __METHOD__
+            ), E_USER_DEPRECATED);
+
             return null;
         }
 
@@ -313,6 +326,17 @@ public function getNormalizedIdentifier($document)
 
     public function getUrlSafeIdentifier($document)
     {
+        // NEXT_MAJOR: Remove the following check and declare "object" as type for argument 1.
+        if (!\is_object($document)) {
+            @trigger_error(sprintf(
+                'Passing other type than object for argument 1 for %s() is deprecated since'
+                .' sonata-project/doctrine-mongodb-admin-bundle 3.x and will be not allowed in version 4.0.',
+                __METHOD__
+            ), E_USER_DEPRECATED);
+
+            return null;
+        }
+
         return $this->getNormalizedIdentifier($document);
     }
 
diff --git a/tests/Model/ModelManagerTest.php b/tests/Model/ModelManagerTest.php
index 2d52a63d..1143254b 100644
--- a/tests/Model/ModelManagerTest.php
+++ b/tests/Model/ModelManagerTest.php
@@ -90,10 +90,19 @@ public function getWrongDocuments(): iterable
         yield ['sonata-project'];
     }
 
+    /**
+     * NEXT_MAJOR: Remove this method.
+     *
+     * @group legacy
+     */
     public function testGetNormalizedIdentifierNull(): void
     {
         $manager = new ModelManager($this->registry, $this->propertyAccessor);
 
+        $this->expectDeprecation(
+            'Passing null as argument 1 for Sonata\DoctrineMongoDBAdminBundle\Model\ModelManager::getNormalizedIdentifier() is deprecated since sonata-project/doctrine-mongodb-admin-bundle 3.x and will be not allowed in version 4.0.'
+        );
+
         $this->assertNull($manager->getNormalizedIdentifier(null));
     }
 
@@ -335,10 +344,19 @@ public function testGetModelInstanceForProtectedDocument(): void
         $this->assertInstanceOf(ProtectedDocument::class, $model->getModelInstance(ProtectedDocument::class));
     }
 
+    /**
+     * NEXT_MAJOR: Remove this method.
+     *
+     * @group legacy
+     */
     public function testFindBadId(): void
     {
         $model = new ModelManager($this->registry, $this->propertyAccessor);
 
+        $this->expectDeprecation(
+            'Passing null as argument 1 for Sonata\DoctrineMongoDBAdminBundle\Model\ModelManager::find() is deprecated since sonata-project/doctrine-mongodb-admin-bundle 3.x and will be not allowed in version 4.0.'
+        );
+
         $this->assertNull($model->find('notImportant', null));
     }
 
@@ -351,10 +369,19 @@ public function testGetUrlSafeIdentifierException(): void
         $model->getNormalizedIdentifier(new \stdClass());
     }
 
+    /**
+     * NEXT_MAJOR: Remove this method.
+     *
+     * @group legacy
+     */
     public function testGetUrlSafeIdentifierNull(): void
     {
         $model = new ModelManager($this->registry, $this->propertyAccessor);
 
+        $this->expectDeprecation(
+            'Passing null as argument 1 for Sonata\DoctrineMongoDBAdminBundle\Model\ModelManager::getNormalizedIdentifier() is deprecated since sonata-project/doctrine-mongodb-admin-bundle 3.x and will be not allowed in version 4.0.'
+        );
+
         $this->assertNull($model->getNormalizedIdentifier(null));
     }