The changeType property belongs to the change event, not to the form submit event.

According to [Serge Insas](https://stackoverflow.com/a/17751347/1595451), "to know what value is returned in the event info" instead of `event.changeType` use `Utilities.jsonStringify(event)`.

#References
 - [Event Objects - Google Apps Script](https://developers.google.com/apps-script/guides/triggers/events)
 - [Google Apps Event changeType undefined in Google Sheet - Stack Overflow](https://stackoverflow.com/questions/17750589/google-apps-event-changetype-undefined-in-google-sheet)