The null that meant three different things
Not-yet-loaded, absent, and explicitly-cleared share one representation, and the UI has to guess.
api-design
4 posts
Offset pagination loses rows while you read, and the user never knows
An insert on page 1 shifts every later offset. A keyset cursor is data, not a position.
Idempotency is a product decision before it is a technical one
Deciding what counts as the same request is a business question. The key is the easy part.
Your error message is an API, and changing it breaks someone
Somebody is grepping your log line, matching on your message, or alerting on its text.