JsonPreprocessor harmed by comnposite strings

[HolQue]

This works:

"index"     : 0,
"listParam" : [0,1,2],
"value"     : "A",
"dictParam" : {"A" : 1, "B" : 2},
"param1" : {"kA" : ${listParam}[${index}],
            "kB" : "${dictParam}[${value}]"}

kB has string value '1'

I add '-X' to the string value of kB:

"param1" : {"kA" : ${listParam}[${index}],
            "kB" : "${dictParam}[${value}]-X"}

Result:

Expecting ',' delimiter: line ...

But expected:

kB has string value '1-X'