add migration to clean class data

cfl_common/common/migrations/0053_clean_class_data.py

@@ -0,0 +1,17 @@
+from django.db import migrations, models
+
+def clean_dirty_data(apps: Apps, *args):
+    Class = apps.get_model("common", "Class")
+
+    Class.objects.filter(
+        creation_time.year = 2015
+    ).update(creation_time = null)
+
+class Migration(migrations.Migration):
+    dependencies = [("common", "0052_add_cse_fields")],
+    operations = [
+        migrations.RunPython(
+            code=clean_dirty_data,
+            reverse_code=migrations.RunPython.noop,
+        ),
+    ]