Django/venv/lib/python3.7/site-packages/django/contrib/gis/apps.py

from django.apps import AppConfig
from django.core import serializers
from django.utils.translation import gettext_lazy as _


class GISConfig(AppConfig):
    name = 'django.contrib.gis'
    verbose_name = _("GIS")

    def ready(self):
        serializers.BUILTIN_SERIALIZERS.setdefault('geojson', 'django.contrib.gis.serializers.geojson')