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

apps/logs/migrations/0002_replace_null_by_blank.py

@@ -0,0 +1,17 @@
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('logs', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.RunSQL(
+            "UPDATE logs_changelog SET previous = '' WHERE previous IS NULL;"
+        ),
+        migrations.RunSQL(
+            "UPDATE logs_changelog SET data = '' WHERE data IS NULL;"
+        ),
+    ]

apps/logs/migrations/0003_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 = [
+        ('logs', '0002_replace_null_by_blank'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='changelog',
+            name='data',
+            field=models.TextField(blank=True, default='', verbose_name='new data'),
+        ),
+        migrations.AlterField(
+            model_name='changelog',
+            name='previous',
+            field=models.TextField(blank=True, default='', verbose_name='previous data'),
+        ),
+    ]