Add __str__ to models, remove null=True in CharField and TextField

apps/note/migrations/0003_replace_null_by_blank.py

@@ -0,0 +1,17 @@
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('note', '0002_create_special_notes'),
+    ]
+
+    operations = [
+        migrations.RunSQL(
+            "UPDATE note_note SET inactivity_reason = '' WHERE inactivity_reason IS NULL;"
+        ),
+        migrations.RunSQL(
+            "UPDATE note_transaction SET invalidity_reason = '' WHERE invalidity_reason IS NULL;"
+        ),
+    ]

apps/note/migrations/0004_remove_null_tag_on_charfields.py

@@ -0,0 +1,23 @@
+# Generated by Django 2.2.16 on 2020-09-06 19:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('note', '0003_replace_null_by_blank'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='note',
+            name='inactivity_reason',
+            field=models.CharField(blank=True, choices=[('manual', 'The user blocked his/her note manually, eg. when he/she left the school for holidays. It can be reactivated at any time.'), ('forced', "The note is blocked by the the BDE and can't be manually reactivated.")], default='', max_length=255),
+        ),
+        migrations.AlterField(
+            model_name='transaction',
+            name='invalidity_reason',
+            field=models.CharField(blank=True, default='', max_length=255, verbose_name='invalidity reason'),
+        ),
+    ]