[From string (line 13) ]                                                               
                                                                                       
@startuml                                                                              
!unquoted function $lookup($id)                                                        
!$data={"participants":[                                                               
{"id": "cm", "label": "label cm", "desc": "desc cm"},                                  
{"id": "tm", "label": "label tm", "desc": "desc tm"},                                  
{"id": "am", "label": "label am", "desc": "desc am"}                                   
]}                                                                                     
!foreach $part in $data.participants                                                   
  !if $part.id == $id                                                                  
  :id=$part.id \nlabel=$part.label \ndesc=$part.desc;                                  
  !endif;                                                                              
!endfor                                                                                
!endfunction                                                                           
^^^^^                                                                                  
 This function does not have any !return directive. Declare it as a procedure instead ?