make it optional to specify speaker_event conflicts

src/program/migrations/0099_alter_speaker_event_conflicts.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.2.5 on 2021-08-15 20:03
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("program", "0098_auto_20200811_1015"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="speaker",
+            name="event_conflicts",
+            field=models.ManyToManyField(
+                blank=True,
+                help_text="The Events this person wishes to attend. The AutoScheduler will avoid conflicts.",
+                related_name="speaker_conflicts",
+                to="program.Event",
+            ),
+        ),
+    ]

src/program/models.py

@@ -1540,6 +1540,7 @@ class Speaker(CampRelatedModel):
     event_conflicts = models.ManyToManyField(
         "program.Event",
         related_name="speaker_conflicts",
+        blank=True,
         help_text="The Events this person wishes to attend. The AutoScheduler will avoid conflicts.",
     )