[bug report] FIVEx search breaks with poor error messaging on certain genes

[abought]

In a public thread, Eric Fauman notes that FIVEx search fails when looking for the gene PLA2G10.

Initial workup traces the error to the "suggest best region" code, such as this URL:
https://fivex.sph.umich.edu/api/data/best/region/16/14172545-15194669/?gene_id=ENSG00000069764.9

The endpoint in question appears to be powered by a "best variant" database from credible sets: pip.best.variant.summary.sorted.indexed.sqlite3.db. The gene ID does not appear to be in the database (confirmed using the Chr16 merged data file for credible sets), so the endpoint generates a 400 error (with poor error messaging) here:

fivex/fivex/model.py

Line 124 in 51e449a

return abort(400)

Suggested options:

• Improve error messaging to explain why some searches don't yield results
• Are there other ways to express the search within a region that might yield nearby results?

[abought]

The current error messaging is quite user-unfriendly, because the error response returns a 400 with no user-facing message (and the UI seems to rely on whatever message was sent from the server to describe the error). See below example, based on the ENSG version of the gene name.