♻️(models) allow null titles on documents

We want to make it as fast as possible to create a new document.
We should not have any modal asking the title before creating the
document but rather show an "untitle document" title and let the
owner set it on the already created document.

src/backend/core/tests/documents/test_api_documents_create.py

@@ -26,7 +26,7 @@ def test_api_documents_create_anonymous():
     assert not Document.objects.exists()
 
 
-def test_api_documents_create_authenticated():
+def test_api_documents_create_authenticated_success():
     """
     Authenticated users should be able to create documents and should automatically be declared
     as the owner of the newly created document.
@@ -50,6 +50,21 @@ def test_api_documents_create_authenticated():
     assert document.accesses.filter(role="owner", user=user).exists()
 
 
+def test_api_documents_create_authenticated_title_null():
+    """It should be possible to create several documents with a null title."""
+    user = factories.UserFactory()
+
+    client = APIClient()
+    client.force_login(user)
+
+    factories.DocumentFactory(title=None)
+
+    response = client.post("/api/v1.0/documents/", {}, format="json")
+
+    assert response.status_code == 201
+    assert Document.objects.filter(title__isnull=True).count() == 2
+
+
 def test_api_documents_create_force_id_success():
     """It should be possible to force the document ID when creating a document."""
     user = factories.UserFactory()