I had the same error today after some serious faults within my intranet and needed restarts of the backbone components (the plugin has been working before since months without any errors now) .
Root couse & how fixed:
Looking into the variables pages (values of hue lights), one of the extended color light has had a ‘ct’ value of ‘null’ which isn’t in the expected range of 153-500 of course (i guess this happenend due to not reachable or somethig like this). BTW: This is the only hue light which is behind a switchable power socket-outlet and therefore most times disconnected from the power-net).
Switching the light on resolved the issue.