When a NullStepperMotor is created in Simulator and GenericRepRap it is created with the motor ID numbers set as 'X', 'Y', and 'Z'. This is wrong, it should be 1, 2 and 3. If you look at the other classes derived from GenericStepperMotor they are all correctly created.
Actually it would be better to have an enum, then it would be much clearer.
