I got a reusable sub process inside a multiple instance node

The variable from multiple instance node is called "item"

the data type for "item" is java.util.Map

I want to use a value from this "item" for Called Element field in Reusable Sub Process

so I try to write

item["myvalueName"]

But it gave validation error and I cant save

then I try again with

#

{item["myvalueName"]}

And again it gave validation error and I cannot save.

Attached the server log, process definition, and screenshots

I use Web Designer from JBPM5.4 Final Full Installer.

I have downloaded the source code for the designer from git, but I still have no idea which part of the designer I should modify to resolve this issue?

Regards,

Thomas Setiabudi