Django's Image Field and Google app engine

I have a django app deployed on google cloud platform. I also have the same app deployed on heroku (It works fine). I have a model in my code that looks like this :

class Notification(models.Model):
## other fields 
qrcode = models.ImageField(null=True, blank=True, default=None)

When I pass this model to the serializer, I got a status code 500.

I googled it and find some answers referring to PIL library or some needed configuration in the Google Cloud App Engine in order to support ImageField.

NOTE :

django-admin on heroku looks like this:

django-admin on google cloud looks like this :

Does anyone know what to do in this case?

Thanks in advance.