Make biography optional

contour/migrations/0055_auto_20190513_1058.py

+# Generated by Django 2.1.1 on 2019-05-13 10:58
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('contour', '0054_auto_20190425_0938'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='event',
+            name='project',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='events', to='contour.Project'),
+        ),
+        migrations.AlterField(
+            model_name='participant',
+            name='name_nl',
+            field=models.CharField(blank=True, max_length=255, null=True),
+        ),
+    ]

contour/migrations/0056_auto_20190513_1101.py

+# Generated by Django 2.1.1 on 2019-05-13 11:01
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('contour', '0055_auto_20190513_1058'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='participant',
+            name='bio_nl',
+            field=models.TextField(blank=True, null=True, verbose_name='Biography'),
+        ),
+    ]