Serializing "complex" field returns None instead of the value since 3.4

[aaugustin]

(Not a great title — I hope the description will clarify.)

Steps to reproduce

First: pip install django-phonenumber-field

With the following model and serializer:

from django.db.models import Model
from phonenumber_field.modelfields import PhoneNumberField
from rest_framework.serializers import ModelSerializer

class PhoneModel(Model):
    number = PhoneNumberField()

class PhoneSerializer(ModelSerializer):
    class Meta:
        model = PhoneModel
        fields = ['number']

Expected behavior

This test used to pass (until version 3.3.3):

def test_phone_serializer():
    phone = models.PhoneModel(number='+33610293847')
    data = models.PhoneSerializer(phone).data
    assert data['number'] == '+33610293847'

Actual behavior

The test fails (since version 3.4) with:

    def test_phone_serializer():
        phone = models.PhoneModel(number='+33610293847')
        data = models.PhoneSerializer(phone).data
>       assert data['number'] == '+33610293847'
E       assert None == '+33610293847'

Analysis

I bisected this regression to 9c996d7.

As far as I can tell, DRF used to get the string representation of the field and no longer does.

(Pdb) phone.number
PhoneNumber(country_code=33, national_number=610293847, extension=None, italian_leading_zero=None, number_of_leading_zeros=None, country_code_source=1, preferred_domestic_carrier_code='')
(Pdb) str(phone.number)
'+33610293847'

[aaugustin]

Actually you seem to be missing a return here: 9c996d7#diff-ce493f71b3679e91b72126c168670399R128