code: private Map<Optional<Executor>, List<ExecutableFlow>> getFlowToExecutorMap() {
      final HashMap<Optional<Executor>, List<ExecutableFlow>> exFlowMap = new HashMap<>();
      try {
        for (final Pair<ExecutionReference, ExecutableFlow> runningFlow : this
            .executorLoader.fetchActiveFlows().values()) {
          final Optional<Executor> executor = runningFlow.getFirst().getExecutor();
          List<ExecutableFlow> flows = exFlowMap.get(executor);
          if (flows == null) {
            flows = new ArrayList<>();
            exFlowMap.put(executor, flows);
          }
          flows.add(runningFlow.getSecond());
        }
      } catch (final ExecutorManagerException e) {
        logger.error("Failed to get flow to executor map");
      }
      return exFlowMap;
    }
docs: Groups Executable flow by Executors to reduce number of REST calls.
  
  @return executor to list of flows map