Python 3, Django 1.8.5, Postgres
I have a model Sites that has been working fine. I recently tried to add a field, airport_code, and migrate the data.>
Stuck into this issue recently.
In my case, I added a reference to a non-existing field in the code, then I came to the model file and added the new field, then tried to run makemigrations command which thrown the above error.
So I went to the stack trace all the way up and found the newly added reference was the problem. commented that out, ran makemigrations and voila.