NoMethodError

What happened

• The serializer calls claim_denied_by for every item whose status is denied.
• That method takes the latest audit and reads user_id without checking that an audit exists.
• A denied item with no audits gives nil, so the index action returns a 500.
• There were 6 events for 5 users over 56 days. That fits a few bad records and not a path that always fails.

What to do next

1. Code fix In app/models/member_billing_item.rb, change claim_denied_by to use `audits.reorder(id: :desc).first&.user_id`. Return nil if the user_id is nil. Use `User.find_by(id: user_id)&.name` for the lookup.
2. Query Placeholder. Replace the status subquery with the real KEY_BIS_CLAIM_DENIED value to list denied items that have no audits. Check the table and column names against db/schema.rb first.

   SELECT mbi.id, mbi.status, mbi.updated_at FROM member_billing_items mbi LEFT JOIN audits a ON a.auditable_type = 'MemberBillingItem' AND a.auditable_id = mbi.id WHERE mbi.status = (SELECT id FROM reference_data WHERE false) GROUP BY mbi.id HAVING COUNT(a.id) = 0;

Queries are shown, never run. Check them before using them on production.