code: public OmemoMessage.Sent encrypt(BareJid recipient, String message)
              throws CryptoFailedException, UndecidedOmemoIdentityException,
              InterruptedException, SmackException.NotConnectedException,
              SmackException.NoResponseException, SmackException.NotLoggedInException {
          synchronized (LOCK) {
              Set<BareJid> recipients = new HashSet<>();
              recipients.add(recipient);
              return encrypt(recipients, message);
          }
      }
docs: OMEMO encrypt a cleartext message for a single recipient.
  Note that this method does NOT set the 'to' attribute of the message.
  
  @param recipient recipients bareJid
  @param message text to encrypt
  @return encrypted message
  @throws CryptoFailedException                when something crypto related fails
  @throws UndecidedOmemoIdentityException      When there are undecided devices
  @throws InterruptedException
  @throws SmackException.NotConnectedException
  @throws SmackException.NoResponseException
  @throws SmackException.NotLoggedInException