Currently, the documentation only mentions Null Field Type (https://doc.ezplatform.com/en/latest/guide/field_type_reference/#null-field-type).
It should be used with NullConverter as a dummy implementation for Field Types from Legacy Stack, to silence errors in the Platform Stack.
Also, this possibility should be mentioned in the migration guide (https://doc.ezplatform.com/en/latest/migrating/migrating_from_ez_publish/).