code: final KNXFormatException logThrow(LogLevel level, String msg, String excMsg,
  		String item)
  	{
  		final KNXFormatException e =
  			new KNXFormatException(excMsg != null ? excMsg : msg, item);
  		if (excMsg != null)
  			logger.log(level, dpt.getID() + " - " + msg, e);
  		else
  			logger.log(level, dpt.getID() + " - " + msg);
  		return e;
  	}
docs: Helper which logs message and creates a format exception.
  <p>
  Adds the current dpt ID as prefix to log output.
  
  @param level log level
  @param msg log output, exception message if <code>excMsg</code> is
  <code>null</code>
  @param excMsg exception message, if <code>null</code> <code>msg</code> is used
  @param item item in KNXFormatException, might be <code>null</code>