GenericForeignKey regression after #224

[decibyte]

$ pip freeze | grep pylint
pylint==2.3.1
pylint-django==2.0.8
pylint-plugin-utils==0.5

I tested with version 2.0.6, the last version before #224 was merged, and that version doesn't have this issue.

I'm getting a TypeError: 'NoneType' object is not iterable for a model similar to the following example. It's triggered by this line.

# models.py

from django.contrib.contenttypes.fields import GenericForeignKey                
from django.contrib.contenttypes.models import ContentType
from django.db import models

class Ownership(models.Model):
    owner_type = models.ForeignKey(ContentType, models.CASCADE)
    owner_id = models.PositiveIntegerField()
    owner = GenericForeignKey("owner_type", "owner_id")

[decibyte]

Wow, that was quick! Thanks, @atodorov :)