Steps to Reproduce

1. Install Confluence and Team Calendars
2. Set Confluence's timezone to a value that is not considered valid by Team Calendars, using a JVM parameter. For example, "UTC":

   -Duser.timezone=UTC
   

3. Try to import this .ics file into Team Calendars: [^example.ics]

Expected Results

The calendar either imports or displays a reason in the UI why it cannot be imported.

Actual Results

The UI shows no action when the Import button is pressed, and the dialog remains up.
Application logs show that a particular VM file cannot be found:

2018-11-21 20:07:57,826 ERROR [http-nio-8090-exec-4367] [opensymphony.webwork.dispatcher.VelocityResult] doExecute Unable to render Velocity Template, '/com/atlassian/confluence/extra/templates/velocity/calendar3/calendar-import-subcalendar-timeZoneRequired.vm'
...

Notes

From the error, we can see that the VM file does not actually exist where plugin is expecting it. In the Team Calendars JAR file, it is located in a slightly different path:

A related ticket to improve Team Calendars timezone detection has been raised here: CONFSERVER-57757

Workaround

Ensure that the .ics file contains a valid timezone. Definitions and examples below:

• https://tools.ietf.org/html/rfc5545#section-3.6.5
• https://stackoverflow.com/questions/35645402/how-to-specify-timezone-in-ics-file-which-will-work-efficiently-with-google-outl