code: public void checkFile(Query query) throws ValidationException {
  		if (!outputFile.exists()) {
  			if (loggers.containsKey("/dev/null")) {
  				logger = loggers.get("/dev/null");
  			} else {
  				try {
  					logger = initLogger("/dev/null");
  					loggers.put("/dev/null", logger);
  				} catch (IOException e) {
  					throw new ValidationException("Failed to setup logback", query, e);
  				}
  			}
  
  			if (loggers.containsKey(outputFile.getAbsolutePath())) {
  				loggers.remove(outputFile.getAbsolutePath());
  			}
  			return;
  		} else if (loggers.containsKey(outputFile.getAbsolutePath())) {
  			logger = loggers.get(outputFile.getAbsolutePath());
  			return;
  		}
  
  		try {
  			logger = initLogger(outputFile.getAbsolutePath());
  			loggers.put(outputFile.getAbsolutePath(), logger);
  		} catch (IOException e) {
  			throw new ValidationException("Failed to setup logback", query, e);
  
  		}
  	}
docs: Creates the logging. Nagios doesn't start if the external command pipe
  exists, so we write to /dev/null until we have it available.
  From the official documentation:
  <blockquote>
  The external command file is implemented as a named pipe (FIFO),
  which is created when Nagios starts and removed when it shuts down.
  If the file exists when Nagios starts,
  the Nagios process will terminate with an error message.
  http://nagios.sourceforge.net/docs/3_0/configmain.html#command_file
  </blockquote>