code: public void removeDevice(String id) throws UnknownDeviceException, NullIdException {
  		if ((id == null) || (id.trim().equals(""))) {
  			throw new NullIdException();
  		}
  		if (this.devices.containsKey(id)) {
  			this.devices.remove(id);
  		} else {
  			throw new UnknownDeviceException();
  		}
  	}
docs: Remove a device
  @param id The device id
  @throws UnknownDeviceException
  @throws NullIdException