Problem in Relay Actuator

[JeJ]

I have a question about the Relay Actuator code.
In line 43 it says "digitalWrite(message.sensor-1+RELAY_1, message.getBool()?RELAY_ON:RELAY_OFF);"

The part "message.sensor-1+RELAY_1" doesn't seem to work for me, if i change it to "message.sensor" the digitalWrite works.

/Jesper