[From string (line 6) ]                                                                
                                                                                       
@startuml                                                                              
!function addService($part, $service, $as)                                             
    !if %variable_exists($part)                                                        
        control "$service" as $as                                                      
    !endif                                                                             
!endfunction                                                                           
^^^^^                                                                                  
 This function does not have any !return directive. Declare it as a procedure instead ?