code: public static <T> ParallelBatch<T> of(final TraceContext context, Iterable<? extends Promise<T>> promises) {
      return ParallelBatch.of(promises)
          .execInit(execution -> execution.add(RatpackCurrentTraceContext.wrap(context)));
    }
docs: Create a {@link TracedParallelBatch} for list of {@link Promise}s,
  with the specified trace context.
  
  @param context the trace context
  @param promises an iterable of Promises
  @param <T> the type of value produced by each promise
  
  @return an instance of {@link ParallelBatch}.