Refs #25165 -- Fixed JSON serialization for add/edit popup in the admin.

Forwardport of test in o839d71d8562abe0b245024e55ca1d02a45e58fd from stable/1.9.x
(refs #25997).

tests/admin_views/models.py

@@ -4,6 +4,7 @@ from __future__ import unicode_literals
 import datetime
 import os
 import tempfile
+import uuid
 
 from django.contrib.auth.models import User
 from django.contrib.contenttypes.fields import (
@@ -956,3 +957,15 @@ class ReferencedByGenRel(models.Model):
 
 class GenRelReference(models.Model):
     references = GenericRelation(ReferencedByGenRel)
+
+
+class ParentWithUUIDPK(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    title = models.CharField(max_length=100)
+
+    def __str__(self):
+        return str(self.id)
+
+
+class RelatedWithUUIDPKModel(models.Model):
+    parent = models.ForeignKey(ParentWithUUIDPK, on_delete=models.CASCADE)