docs: public ExecutorService getOrBuildWorkerExecutor(Map<String, ExecutorService> boundWorkerExecutors)
      {
          if (workerExecutorKey.isPresent()) {
              checkState(!workerExecutor.isPresent(),
                         "Worker executor key should not be set along with a specific worker executor instance");
              checkState(!workerThreads.isPresent(),
                         "Worker executor key should not be set along with a number of worker threads");
              checkState(!maxQueuedRequests.isPresent(),
                         "When using a custom executor, handling maximum queued requests must be done manually");
  
              String key = workerExecutorKey.get();
              checkArgument(boundWorkerExecutors.containsKey(key),
                            "No ExecutorService was bound to key '" + key + "'");
              ExecutorService executor = boundWorkerExecutors.get(key);
              checkNotNull(executor, "WorkerExecutorKey maps to null");
              return executor;
          }
          else if (workerExecutor.isPresent()) {
              checkState(!workerThreads.isPresent(),
                         "Worker executor should not be set along with number of worker threads");
              checkState(!maxQueuedRequests.isPresent(),
                         "When using a custom executor, handling maximum queued requests must be done manually");
  
              return workerExecutor.get();
          }
          else {
              return makeDefaultWorkerExecutor();
          }
      }