addons-frontend: 500 error when accessing "/fi/firefox/tag/prefs.js"

For QA: URLs like /fi/firefox/tag/prefs.js should return a 404 in -dev and -stage. CDN domains are listed below (see: https://github.com/mozilla/addons-frontend/issues/7962#issuecomment-514283933).

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Describe the problem and steps to reproduce it:

We see a bunch 500 errors when /fi/firefox/tag/prefs.js endpoint is accessed.

Is this something that can be fixed?

What happened?

Saw a bunch 500 in access logs.

1556827602.237 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=578&appver=30.0&atype=9&page=19616&cat=128 HTTP/1.1" 500 12110 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.658 0.658 "-"
1556827689.262 "157.55.39.139" "GET /fi/firefox/tag/prefs.js?appver=any&atype=9&page=20089&cat=106 HTTP/1.1" 500 11999 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.677 0.677 "-"
1556827693.765 "157.55.39.147" "GET /fi/firefox/tag/prefs.js?platform=all&appver=624&atype=9&page=17763&cat=104 HTTP/1.1" 500 12105 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.703 0.703 "-"
1556827698.408 "157.55.39.223" "GET /fi/firefox/tag/prefs.js?atype=9&page=19945&cat=100 HTTP/1.1" 500 11899 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.725 0.725 "-"
1556828056.074 "157.55.39.139" "GET /fi/firefox/tag/prefs.js?appver=31.0&atype=9&page=20226 HTTP/1.1" 500 11915 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.655 0.655 "-"
1556828119.266 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?appver=30.0&atype=9&page=20022&cat=100 HTTP/1.1" 500 12002 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.675 0.675 "-"
1556828940.759 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?appver=30.0&atype=9&page=17483&cat=124 HTTP/1.1" 500 12002 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.769 0.769 "-"
1556828943.574 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=all&atype=9&page=17405&cat=114 HTTP/1.1" 500 12007 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.698 0.698 "-"
1556828945.203 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=linux&appver=30.0&atype=9&page=20051&cat=106 HTTP/1.1" 500 12116 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.698 0.698 "-"
1556829193.473 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=all&appver=392&atype=9&page=20226&cat=126 HTTP/1.1" 500 12105 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.881 0.881 "-"
1556829615.197 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=all&atype=9&page=17566&cat=120 HTTP/1.1" 500 12007 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.960 0.960 "-"
1556829677.375 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=all&appver=31.0&atype=9&page=19904&cat=106 HTTP/1.1" 500 12110 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.699 0.699 "-"
1556829685.730 "157.55.39.223" "GET /fi/firefox/tag/prefs.js?platform=all&appver=31.0&atype=9&page=19906&cat=106 HTTP/1.1" 500 12110 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.663 0.663 "-"
1556829689.022 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?appver=4.0&atype=9&page=20231&cat=100 HTTP/1.1" 500 11999 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.018 0.018 "-"
1556830161.315 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=all&appver=28.0&atype=9&page=19650 HTTP/1.1" 500 12021 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.664 0.664 "-"
1556830457.208 "157.55.39.139" "GET /fi/firefox/tag/prefs.js?platform=all&atype=9&page=17826&cat=110 HTTP/1.1" 500 12007 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.969 0.969 "-"
1556830466.475 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?platform=all&appver=3.5&atype=9&page=17536&cat=102 HTTP/1.1" 500 12105 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.771 0.771 "-"
1556831181.480 "157.55.39.139" "GET /fi/firefox/tag/prefs.js?platform=linux&appver=31.0&atype=9&page=6&cat=124 HTTP/1.1" 500 12102 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.690 0.690 "-"
1556831185.488 "157.55.39.223" "GET /fi/firefox/tag/prefs.js?appver=3.5&atype=9&page=19135&cat=406 HTTP/1.1" 500 11999 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.646 0.646 "-"
1556831981.506 "157.55.39.139" "GET /fi/firefox/tag/prefs.js?appver=29.0&atype=9&page=17402&cat=112 HTTP/1.1" 500 12002 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.016 0.016 "-"
1556832252.400 "157.55.39.223" "GET /fi/firefox/tag/prefs.js?appver=20.0&atype=9&page=20213&cat=122 HTTP/1.1" 500 12002 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.660 0.660 "-"
1556832832.087 "207.46.13.153" "GET /fi/firefox/tag/prefs.js?appver=26.0&atype=9&page=17823&cat=126 HTTP/1.1" 500 12002 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.758 0.758 "-"
1556832836.209 "157.55.39.139" "GET /fi/firefox/tag/prefs.js?appver=30.0&atype=9&page=19613&cat=128 HTTP/1.1" 500 12002 "-" "Mozilla/5.0 (compatible; bingbot/2.0; +http://www.bing.com/bingbot.htm)" 0.697 0.697 "-"

What did you expect to happen?

500 rate is one of the metrics that alerts operations, and we hope there is less noise in it if possible.

Anything else we should know?

n/a