bugfix missing username from backlinked user

djangoldp/models.py

 import json
+import uuid
 from urllib.parse import urlparse
 from django.conf import settings
+from django.core.exceptions import ObjectDoesNotExist
 from django.contrib.auth import get_user_model
 from django.db import models
 from django.db.models import BinaryField, DateField
@@ -150,8 +152,10 @@ class Model(models.Model):
         try:
             print('get_or_create ' + str(model) + ' backlink ' + str(urlid))
             return model.objects.get(urlid=urlid)
-        except model.DoesNotExist:
+        except ObjectDoesNotExist:
             print('creating..')
+            if model is get_user_model():
+                field_tuples['username'] = uuid.uuid4()
             return model.objects.create(urlid=urlid, allow_create_backlink=False, **field_tuples)
 
     @classonlymethod