fix: add null protection for locations field

[davidgamez]

Summary:

Fix #799

Expected behavior:

Having null values in locations don't crash the app.

Testing tips:

Follow steps in #799

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• Run the unit tests with ./scripts/api-tests.sh to make sure you didn't break anything
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• Linked all relevant issues
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[github-actions]

Preview Firebase Hosting URL: https://mobility-feeds-dev--pr-800-ldokw9n4.web.app

[davidgamez]

[jcpitre]

@davidgamez I think we need to go around and correct other cases where this happens. e.g. :

mobility-feed-api/web-app/src/app/screens/Feed/FeedSummary.tsx

Line 240 in 73ea4bc

{feed?.data_type === 'gtfs' &&

We get an NPE and a white page when trying to display the summary for tld-933

[jcpitre]

Can't we use locations == null to cover both cases? Why do we use a strict equality operator?
(I know its been closed for a while, but I suspect we'll have similar repairs to do. e.g. this comment)

[isabelle-dr]

Also a blank page for https://mobilitydatabase.org/feeds/tld-823

[isabelle-dr]

Other one https://mobilitydatabase.org/feeds/tld-947

[emmambd]

@isabelle-dr It's because you're logged in as a mobilitydata user. It's not a user facing issue - those are unpublished feeds. I can give you an overview of how this new workflow operates on Friday.