When I use the function 'handle report' by not changing the status, but sending an alert to the reporter then I get the error:
ERROR
Please enter a valid message.
There is no field that needs to be filled with a valid message.
Sending an alert to the author is only valid if you specify a Rejected or Resolved status. Otherwise it would be considered to be a comment only. So if no comment is specified, that's the message that needs to be entered.