Вернуть None из Enum

Question

У меня есть простое перечисление:

from enum import Enum


class ColorEnum(Enum):
    RED = 1
    GREEN = 2
    BLUE = 3

    @classmethod
    def _missing_(cls, value):
        if value is None:
            return None
        super()._missing_(value)

Как вы можете видеть, если None передается в ColorEnum init, он возвращает None. Это работает для Python 3.6. Но не работает для Python 3.7, когда происходит сбой с ValueError:

ValueError: None не является допустимым ColorEnum

Для Python 3.6 метода __new__ выглядит следующим образом:

class Enum(metaclass=EnumMeta):
    """Generic enumeration.

    Derive from this class to define new enumerations.

    """
    def __new__(cls, value):
        # all enum instances are actually created during class construction
        # without calling this method; this method is called by the metaclass'
        # __call__ (i.e. Color(3) ), and by pickle
        if type(value) is cls:
            # For lookups like Color(Color.RED)
            return value
        # by-value search for a matching enum member
        # see if it's in the reverse mapping (for hashable values)
        try:
            if value in cls._value2member_map_:
                return cls._value2member_map_[value]
        except TypeError:
            # not there, now do long search -- O(n) behavior
            for member in cls._member_map_.values():
                if member._value_ == value:
                    return member
        # still not found -- try _missing_ hook
        return cls._missing_(value)

Для Python 3.7:

class Enum(metaclass=EnumMeta):
    """Generic enumeration.

    Derive from this class to define new enumerations.

    """
    def __new__(cls, value):
        # all enum instances are actually created during class construction
        # without calling this method; this method is called by the metaclass'
        # __call__ (i.e. Color(3) ), and by pickle
        if type(value) is cls:
            # For lookups like Color(Color.RED)
            return value
        # by-value search for a matching enum member
        # see if it's in the reverse mapping (for hashable values)
        try:
            return cls._value2member_map_[value]
        except KeyError:
            # Not found, no need to do long O(n) search
            pass
        except TypeError:
            # not there, now do long search -- O(n) behavior
            for member in cls._member_map_.values():
                if member._value_ == value:
                    return member
        # still not found -- try _missing_ hook
        try:
            exc = None
            result = cls._missing_(value)
        except Exception as e:
            exc = e
            result = None
        if isinstance(result, cls):
            return result
        else:
            ve_exc = ValueError("%r is not a valid %s" % (value, cls.__name__))
            if result is None and exc is None:
                raise ve_exc
            elif exc is None:
                exc = TypeError(
                        'error in %s._missing_: returned %r instead of None or a valid member'
                        % (cls.__name__, result)
                        )
            exc.__context__ = ve_exc
            raise exc

Поэтому я хотел бы получить None, если None передан init. Как мне это заархивировать?