code: public List<RequestFuture<?>> broadcast(WebhookMessage message)
      {
          Checks.notNull(message, "Message");
          RequestBody body = message.getBody();
          final List<RequestFuture<?>> callbacks = new ArrayList<>(webhooks.size());
          for (WebhookClient webhook : webhooks)
          {
              callbacks.add(webhook.execute(body));
              if (message.isFile()) // for files we have to make new data sets
                  body = message.getBody();
          }
          return callbacks;
      }
docs: Sends the provided {@link net.dv8tion.jda.webhook.WebhookMessage WebhookMessage}
  to all registered {@link net.dv8tion.jda.webhook.WebhookClient WebhookClients}.
  
  <p>Hint: Use {@link net.dv8tion.jda.webhook.WebhookMessageBuilder WebhookMessageBuilder} to
  create a {@link net.dv8tion.jda.webhook.WebhookMessage WebhookMessage} instance!
  
  @param  message
  The message that should be sent to the clients
  
  @throws java.lang.IllegalArgumentException
  If any of the provided arguments is {@code null}
  @throws java.util.concurrent.RejectedExecutionException
  If any of the receivers has been shutdown
  
  @return A list of {@link java.util.concurrent.Future Future} instances
  representing all message tasks.