Serializer IntegerField will not accept null values even if allow_null=True

[dralley]

The serializer looks like this

class RepositorySerializer(ModelSerializer):
    # blah blah

    retained_versions = serializers.IntegerField(
        allow_null=True,
        required=False,
        min_value=1,  # not needed to reproduce
    )

    # blah blah

When POSTing or PATCHing, integer values work fine. However, despite allow_null=True, null values are rejected.

{
    "retained_versions": [
        "A valid integer is required."
    ]
}

Checklist

• Raised initially as discussion #...
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.