Return nil for strange FT 500 errors

[LindseySaari]

Summary

On occasion, the v0/feature_toggles endpoint returns 500 errors in large groups. See this example of 368 errors. This also happens over a random cadence that doesn't match up to any specific patterns (We've checked RDS connectivity issues, networking, timeouts, etc)

I added some logging around the issue and the response is that session[:token] is ALWAYS empty and when we do the Session.find(session[:token]), it returns 1 for some reason. It's possible this is a bug in the underlying Redis Namespace gem, etc.

The conditional added here will check if the expected response is not a hash AND if the session[:token] is empty, it will return nil. This will cover the case that we are experiencing.

After doing some investigation, this has been occurring for 7+ months according to Sentry. See comment in ticket here, so it doesn't appear to be an issue that was introduced during the EKS rollout.

Related issue(s)

https://app.zenhub.com/workspaces/platform-tech-team-1-633af4074573d06c3cda142a/issues/gh/department-of-veterans-affairs/va.gov-team/57316

Research

It's also possible that this is somehow related to the session reset (maybe a race condition where the session is being reset, but the feature_toggles endpoint is hit at the same time?) During the this example where FT errors are seen, there are MANY reset_session logs.