django v2 compatible: tests needed

src/reminders/models.py

@@ -3,6 +3,6 @@ from django.db import models
 
 class Reminder(models.Model):
 
-    document = models.ForeignKey("documents.Document")
+    document = models.ForeignKey("documents.Document",on_delete=models.DO_NOTHING)
     date = models.DateTimeField()
     note = models.TextField(blank=True)