User's time-zone being set to blank and defaulting to UTC (GMT 0) in product

Issue Summary

• Users are reporting that their their time-zone has been set to GMT 0 (UTC) in product like Confluencne.
• Checking further, it appears that their time-zone values have been set to blank in their profile.

Steps to Reproduce

1. Check the user's time-zone in product like Confluence, and it would be set to "GMT+0000".
   • https://<SITE-NAME>.atlassian.net/wiki/users/viewmysettings.action
2. Check the account preferences, and the time-zone field is blank.
   • https://id.atlassian.com/manage-profile/account-preferences
   • This causes issues with apps the rely on the time-zone, like Team Calendar.
     • There's another bug for Team Calendar where it caches the time-zone value, and it takes awhile for the time-zone changes to be picked up by Team Calendar.
   • There's also the issue that the daily and weekly update emails are using the UTC time-zone for edit times.

Expected Results

• Customer time-zone values should be set to their correct time-zones that they've set before.

Actual Results

• Customer's time-zone has been updated to blank values.

Workaround

• Manually update the time-zone in account preference.
  • https://id.atlassian.com/manage-profile/account-preferences