The RelayWithButtonActuator sketch at https://github.com/mysensors/MySensorsArduinoExamples/blob/master/examples/RelayWithButtonActuator/RelayWithButtonActuator.ino still contains a "S_LIGHT". This is not present in the API page at https://www.mysensors.org/download/sensor_api_20.
IIRC, this was renamed to S_BINARY.