Issue when use #mentions for ticket notifications

[justpbk]

Fatal error: Uncaught InvalidArgumentException: User expected in /var/www/html/bss_support/include/class.user.php:1485 Stack trace: #0 /var/www/html/bss_support/include/plugins/mentioner/class.MentionerPlugin.php(122): UserList->add() #1 /var/www/html/bss_support/include/plugins/mentioner/class.MentionerPlugin.php(62): MentionerBackend->checkThreadTextForMentions() #2 /var/www/html/bss_support/include/class.signal.php(98): MentionerBackend->{closure}() #3 /var/www/html/bss_support/include/class.thread.php(1813): Signal::send() #4 /var/www/html/bss_support/include/class.thread.php(1819): ThreadEntry::create() #5 /var/www/html/bss_support/include/class.thread.php(3006): ThreadEntry::add() #6 /var/www/html/bss_support/include/class.thread.php(3189): ResponseThreadEntry::add() #7 /var/www/html/bss_support/include/class.ticket.php(3365): ObjectThread->addResponse() #8 /var/www/html/bss_support/scp/tickets.php(224): Ticket->postReply() #9 {main} thrown in /var/www/html/bss_support/include/class.user.php on line 1485