Fixes #24 - Set Student.birth_date as nullable in DB

stages/migrations/0003_student_birthdate_nullable.py

@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stages', '0002_add_student_option_ase'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='student',
+            name='birth_date',
+            field=models.DateField(blank=True, null=True, verbose_name='Date de naissance'),
+        ),
+    ]