Test 4: Checking null deletion and new keys...
ERROR: Null deletion or new keys failed:
  - 'app_name' should be preserved from base
  - app_name should be 'MyApp', got 'None'
  - 'new_setting' should be added from override
  - new_setting should be 'added_value', got 'None'
  - version should be '2.0.0' (overridden), got 'None'