Did you ever solve this?
This is an old thread but I had a requirement to do something similar.
Attached is the latest PDF for Expression language.
Or if you want I can give you my docker image that has the conversion tools.
It comes in handy if you ever need to provide deliverables in an isolated environment.
Is the NiFi Expression Language Guide available for PDF download? I'm one
of those old guys who likes things on hard copy so I can highlight, circle
and mark up.. kinda hard to do on my laptop. ;)