docs: public boolean contains(Jid jid) {
          if (jid == null) {
              return false;
          }
          synchronized (entries) {
              for (Iterator<EntityBareJid> i = entries.iterator(); i.hasNext();) {
                  EntityBareJid entry = i.next();
                  if (entry.equals(jid)) {
                      return true;
                  }
              }
          }
          return false;
      }