docs: public void createMailbox(Long proposedHSId, Mailbox mailbox) {
          long hsId = 0;
          if (proposedHSId != null) {
              if (m_siteMailboxes.containsKey(proposedHSId)) {
                  org.voltdb.VoltDB.crashLocalVoltDB(
                          "Attempted to create a mailbox for site " +
                          CoreUtils.hsIdToString(proposedHSId) + " twice", true, null);
              }
              hsId = proposedHSId;
          } else {
              hsId = getHSIdForLocalSite(m_nextSiteId.getAndIncrement());
              mailbox.setHSId(hsId);
          }
  
          addMailbox(hsId, mailbox);
      }