code: public MailInAdapterResult findMail(Mail mail) {
      int indexPosition = Collections.binarySearch(items, mail, MailComparator.INSTANCE);
      boolean containsMail = false;
      Mail found = null;
      if (indexPosition < 0) {
        indexPosition = ~indexPosition;
      } else {
        found = items.get(indexPosition);
        if (found.getId() == mail.getId()) {
          containsMail = true;
        } else {
          containsMail = false;
          found = null;
        }
      }
  
      return new MailInAdapterResult(containsMail, found, indexPosition);
    }
docs: Searches for an equal mail (compares mail id) in the adapter.
  
  @return A {@link MailInAdapterResult} containing the information if the adapter contains that
  mail and at which index position. If the adapter doesn't contain this mail, then the result
  will contain the index position where the mail would be.