json:true writes to body even if there's nothing to write

[guy-mograbi-at-gigaspaces]

when I mark json:true, I see the body is written.

this makes the code not compatible with node version.
in node version I mark json:true to get the response as json. I don't send anything on the body, and I must not write anything on the body (the REST API I use fails if I do, as it expects an empty body).