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1. If you are using the location.state object for contextual navigation, make sure you always provide default values in case the keys are null or undefined to avoid bugs.

2. Always use req.user.user_id instead of req.headers.user_id in the API.

3. If you create a database transaction in an API route, make sure that in every path the code takes the transaction is either rolled back or committed.

Miscellaneous advice

1. If you are doing either the frontend or backend work for a fullstack story, communicate early and frequently with the developer(s) who are working on the other part of the story