handle unset default editions

bookwyrm/migrations/0018_auto_20201128_2142.py

@@ -0,0 +1,24 @@
+# Generated by Django 3.0.7 on 2020-11-28 21:42
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('bookwyrm', '0017_auto_20201128_1849'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='edition',
+            name='parent_work',
+            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.PROTECT, related_name='editions', to='bookwyrm.Work'),
+        ),
+        migrations.AlterField(
+            model_name='tag',
+            name='name',
+            field=models.CharField(max_length=100, unique=True),
+        ),
+    ]