fix: Allow updates with null privacy (#963)

The GraphQL type allows this, but we were trying to access the privacy
regardless of whether it was null or not.

terraso_backend/apps/project_management/graphql/projects.py

@@ -293,13 +293,15 @@ def mutate_and_get_payload(cls, root, info, **kwargs):
         cls.remove_null_fields(kwargs, ["privacy", "measurement_units"])
         if not user.has_perm(Project.get_perm("change"), project):
             cls.not_allowed()
-        kwargs["privacy"] = kwargs["privacy"].value
 
         metadata = {
             "name": kwargs["name"],
-            "privacy": kwargs["privacy"],
             "description": kwargs["description"] if "description" in kwargs else None,
         }
+
+        if privacy := kwargs.get("privacy"):
+            metadata["privacy"] = privacy.value
+
         logger.log(
             user=user,
             action=log_api.CHANGE,

terraso_backend/tests/graphql/mutations/test_projects.py

@@ -185,13 +185,25 @@ def test_update_project_user_is_manager(project, client, project_manager):
     assert content["data"]["updateProject"]["project"]["privacy"] == "PRIVATE"
 
 
-def test_update_project_audit_log(project, client, project_manager):
+@pytest.mark.parametrize(
+    "metadata",
+    [
+        {
+            "name": "test_name",
+            "privacy": "PRIVATE",
+            "description": "A test project",
+        },
+        {
+            "name": "test_name",
+            "description": "A test project",
+        },
+    ],
+)
+def test_update_project_audit_log(metadata, project, client, project_manager):
     input = {
         "id": str(project.id),
-        "name": "test_name",
-        "privacy": "PRIVATE",
-        "description": "A test project",
     }
+    input.update(metadata)
     client.force_login(project_manager)
 
     response = graphql_query(UPDATE_PROJECT_GRAPHQL, input_data=input, client=client)
@@ -204,7 +216,9 @@ def test_update_project_audit_log(project, client, project_manager):
     assert log_result.event == CHANGE.value
     assert log_result.user_human_readable == project_manager.full_name()
     assert log_result.resource_object == project
-    expected_metadata = {"name": "test_name", "privacy": "private", "description": "A test project"}
+    expected_metadata = metadata
+    if "privacy" in expected_metadata:
+        expected_metadata["privacy"] = expected_metadata["privacy"].lower()
     assert log_result.metadata == expected_metadata