Cool, I found it. First of all, this driver is a bit different from the one built into Hubitat. In device edit page, under "Set Color Temperature" button, there are 3 text fields: Color temperature, Level, Transition time. But if you fill them all, it fails because the driver's method has only 1 parameter. Just something to watch out for, if this is work in progress for future driver update. The driver built in Hubitat has just 1 text field - Color temperature, which is fine.
So now the fix:
First I updated line 157 to:
value = rawValue == 0 ? 6535 : (1000000 / rawValue).toInteger()
because on first init, the device reports value 0 and this results in division by zero.
Second, setting the temperature itself - it failed on row 478. By default, transition time is not set. Even when there is check for this in code with nullables, the "no selection" value actually is not null, but "0A00", which fails to convert to integer. Please add check for this value (and do the same as if it's null).
Also, please make the same fixes to Advanced Zigbee RGBW Bulb driver, as it fails on the same.