docs: public JobManagerJobMetricGroup addJob(JobGraph job) {
  		JobID jobId = job.getJobID();
  		String jobName = job.getName();
  		// get or create a jobs metric group
  		JobManagerJobMetricGroup currentJobGroup;
  		synchronized (this) {
  			if (!isClosed()) {
  				currentJobGroup = jobs.get(jobId);
  
  				if (currentJobGroup == null || currentJobGroup.isClosed()) {
  					currentJobGroup = new JobManagerJobMetricGroup(registry, this, jobId, jobName);
  					jobs.put(jobId, currentJobGroup);
  				}
  				return currentJobGroup;
  			} else {
  				return null;
  			}
  		}
  	}