Serialization integrity test
Model setter integrity test
Add raw_data dict to Model
Adjust tests that used Model._data
Keep valid data on multiple validations
Fix test with default value assumption in context
Validate None values only through the required flag
Change ListType `None` and `[]` values expectations
Explicit check for None on `apply_shape`
Always validate model before serialization
Test for required field validation integrity
Validate required fields when no input is given