Allow Student.klass to be null

stages/migrations/0010_nullable_student_klass.py

@@ -0,0 +1,18 @@
+# Generated by Django 1.10 on 2016-08-31 14:48
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stages', '0009_student_archived_text'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='student',
+            name='klass',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='stages.Klass', verbose_name='Classe'),
+        ),
+    ]