fix: Make activity attendees optional

activities/migrations/0006_activity_attendance_optional.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.10 on 2020-04-02 15:57
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('activities', '0005_shrink_name_fields_to_255'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='activity',
+            name='attendance_list',
+            field=models.ManyToManyField(blank=True, related_name='activities', to='people.Person'),
+        ),
+    ]