Disclaimer: This is not an answer to the OP, but I’m explaining why DRF has this behavior

In short, this happens only if you try to POST through HTML form (DRF Web API Console). If you try through POSTMAN Console, it will raise the Validation Error

Why this??

If you inspect the type of request.data in both case, it will be as

| Request Source    | Input data type   |
|------------------ |-----------------  |
| DRF HTML Input    | QueryDict         |
| POSTMAN API call  | dict              |

Where the change happens?

The get_value() method of Field class causing the behavior. In that, a check happens as,

if html.is_html_input(dictionary):
    ....... do something

from that if clause, the EMPTY/BLANK value became False

Solution

Create custom boolean field for your serializer override it’s get_value() method

from rest_framework.fields import empty


class CustomBooleanField(serializers.BooleanField):
    def get_value(self, dictionary):
        return dictionary.get(self.field_name, empty)


class FooSerializer(serializers.ModelSerializer):
    bar = CustomBooleanField(required=True)

    class Meta:
        fields = '__all__'
        model = Foo

Screenshots

1. DRF Web API console


2. POSTMAN API Console

Add extra_kwargs to your ModelSerializer as suggested below.

class FooSerializer(serializers.ModelSerializer):
    class Meta:
        model = Foo
        fields = "__all__"
        extra_kwargs = {'bar': {'required': True}}

This set required=True argument in bar field.

If you have any further questions than please ask to the comments section.