[From string (line 13) ]                                                               
                                                                                       
@startuml                                                                              
!function LineColor() return "#7BFFBD"                                                 
                                                                                       
!function Msg($from, $to, $note = "", $activate = "false")                             
    !if (($activate == "true") || ($activate == "TRUE"))                               
        $from [LineColor()]->> $to ++                                                  
    !else                                                                              
        $from [LineColor()]->> $to                                                     
    !endif                                                                             
                                                                                       
    !if ($note!="")                                                                    
        note left : $note                                                              
!endfunction                                                                           
^^^^^                                                                                  
 This function does not have any !return directive. Declare it as a procedure instead ?