this works for me:
{
"brightness_pct" : payload.brightness,
"hs_color" : payload.hue and payload.saturation ? [payload.hue, payload.saturation]
}
Update:
{
"brightness_pct" : payload.brightness,
"hs_color" : payload.hue != null and payload.saturation != null ? [payload.hue, payload.saturation]
}
This is actually better as it will work if hue or saturation = 0