Suppress error for non-existent page

[bensteinberg]

This changes an error to a 404 when the paginator is asked for a page that doesn't exist. Currently, the error looks like

Internal Server Error: /casebooks/11306-abortion-guns-and-climate-change-reading-group-spring-2024/as-printable-html/17/

EmptyPage at /casebooks/11306-abortion-guns-and-climate-change-reading-group-spring-2024/as-printable-html/17/
That page contains no results

[rebeccacremona]

Ah! This is so great!

Small suggestion: maybe add an info or debug level logging message, indicating which page of which casebook is empty? I don't see us having time to debug why the page is empty, any time soon, but I think if it is empty, that means some bug happened somewhere, and it might be good to leave breadcrumbs for a potential future dev. But no strong feelings.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 76.90%. Comparing base (e997b79) to head (8ca5bb2).

Files	Patch %	Lines
web/main/views.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2044      +/-   ##
===========================================
- Coverage    76.92%   76.90%   -0.02%     
===========================================
  Files           60       60              
  Lines         6995     6998       +3     
===========================================
+ Hits          5381     5382       +1     
- Misses        1614     1616       +2     

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[bensteinberg]

Sure, I'll add logging -- however, my instinct is that this is not from us exposing a bad link, but rather an ill-conceived behavior on the part of a bot; all the hits on the example above are from bingbot.