Serializing ChoiceField doesn't validate the value

[qu3vipon]

I get to know that ChoiceField checks if the value is included with the given choices when saving data.
But the choice validation is skipped when serializing data.

class ChoiceField(Field):
    # ...
    def to_internal_value(self, data):
            if data == '' and self.allow_blank:
                return ''
            try:
                return self.choice_strings_to_values[str(data)]
            except KeyError:
                self.fail('invalid_choice', input=data)

    def to_representation(self, value):
            if value in ('', None):
                return value
            return self.choice_strings_to_values.get(str(value), value)

Is there any reason for DRF is designed this way?