Nonable fields

[smarie]

From #43 :

As of now we seem to have to explicitly declare optionality for the "check type" to skip the type validation in case of a nullable field.

For example:

from typing import Optional

class A:
     field1: Optional[int] = field(check_type=True, default=None)
     field2: Optional[int] = field(check_type=True)

Note that this is completely independent from the fact that a field is optional or mandatory. However the usual python behaviour for typing is to consider nullable all arguments that have a None default value, see https://stackoverflow.com/a/57390124/7262247.

[smarie]

also we should make the value validators (another feature of pyfields) skip validation in case None is passed.

[devashishshankar]

Thanks