Fixed #24302 -- Added DurationField.formfield()

        val = self._get_val_from_obj(obj)

        return '' if val is None else duration_string(val)

    def formfield(self, **kwargs):

        defaults = {

            'form_class': forms.DurationField,

        }

        defaults.update(kwargs)

        return super(DurationField, self).formfield(**defaults)

class EmailField(CharField):

    default_validators = [validators.validate_email]

import datetime

import json

from django import forms

from django.core import exceptions, serializers

from django.db import models

from django.test import TestCase

            "'not a datetime' value has an invalid format. "

            "It must be in [DD] [HH:[MM:]]ss[.uuuuuu] format."

        )

class TestFormField(TestCase):

    # Tests for forms.DurationField are in the forms_tests app.

    def test_formfield(self):

        field = models.DurationField()

        self.assertIsInstance(field.formfield(), forms.DurationField)