code: private List<Long> prepareRecipients(Collection<Recipient> recipients) {
          List<Long> lst = new ArrayList<>();
  
          for (Recipient recipient : recipients) {
              lst.add(recipient.getIen());
          }
  
          return lst;
      }
docs: Prepares a recipient list for passing to an RPC.
  
  @param recipients List of recipients.
  @return List of recipients to pass to RPC.