docs: public Optional<OperatorBackPressureStats> getOperatorBackPressureStats(ExecutionJobVertex vertex) {
  		synchronized (lock) {
  			final OperatorBackPressureStats stats = operatorStatsCache.getIfPresent(vertex);
  			if (stats == null || backPressureStatsRefreshInterval <= System.currentTimeMillis() - stats.getEndTimestamp()) {
  				triggerStackTraceSampleInternal(vertex);
  			}
  			return Optional.ofNullable(stats);
  		}
  	}