How to read and write a concat SpEL default value in switch statement ?

I have a case where I receive SpEL "#CONTRACTLINEGROUPCODE + #STARTDATE +  #ENDDATE" so need to be in the place of default value in switch case. but its currently throwing error the builder can't read [object object] when I have such value.
is there a way to support this ? and also the user be able to write such a thing by selecting multiple (fields/spel variables) as a default value ?