Honeywell Evohome with HE

Hi all,

I am new to home automation & Hubitat (2 days into all of it...). I've managed to install the app & driver as outlined in this thread: Honeywell Evohome

The thermostats for the individual radiators update their temperature, so I think it's a sign that Hubitat at least receives info from the thermostats.

However, I get all sorts of errors similar to the one below when I try to make any changes to the thermostat settings within Hubitat. I am Groovy/Java virgin, so please go gently on me. I am hoping it's a simple fix but I'm pulling my hair out...

Attached are screenshots of one of the errors and relevant bit of code.

If there is an easier way to troubleshoot than post screenshots here, please someone point me in the right direction.