fix: add migration to clean class data

cfl_common/common/migrations/0053_clean_class_data.py

@@ -0,0 +1,24 @@
+from datetime import date
+
+from django.apps.registry import Apps
+from django.db import migrations, models
+
+def clean_early_class_data(apps: Apps, *args):
+    Class = apps.get_model("common", "Class")
+
+    Class.objects.filter(
+        creation_time__date__lt = date(2021, 10, 15)
+    ).update(creation_time = None)
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("common", "0052_add_cse_fields")
+    ]
+
+    operations = [
+        migrations.RunPython(
+            code=clean_early_class_data,
+            reverse_code=migrations.RunPython.noop,
+        ),
+    ]