make more countdown item fields optional in admin

countdown/migrations/0006_auto_20201025_1716.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.1.2 on 2020-10-25 17:16
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('countdown', '0005_countdownitem_recurring_until'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='countdownitem',
+            name='recurring_period',
+            field=models.CharField(blank=True, default='', max_length=64),
+        ),
+        migrations.AlterField(
+            model_name='countdownitem',
+            name='reminder_target',
+            field=models.CharField(blank=True, default='', max_length=64),
+        ),
+    ]