apply some patches from @brookst

src/reminders/migrations/0002_auto_20180824_2018.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.1 on 2018-08-24 20:18
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('reminders', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='reminder',
+            name='document',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.DO_NOTHING, to='documents.Document'),
+        ),
+    ]

src/reminders/models.py

@@ -4,7 +4,7 @@ from django.db import models
 class Reminder(models.Model):
 
     document = models.ForeignKey(
-        "documents.Document", on_delete=models.DO_NOTHING
+        "documents.Document", on_delete=models.PROTECTION
         )
     date = models.DateTimeField()
     note = models.TextField(blank=True)