docs: public PropertyOwner retrieveUserProperties(String strRegistrationKey)
      {
          if ((strRegistrationKey == null) || (strRegistrationKey.length() == 0))
              return this;        // Use default user properties
          UserProperties regKey = (UserProperties)m_htRegistration.get(strRegistrationKey);
          if (regKey == null)
              regKey = new UserProperties(this, strRegistrationKey);
          regKey.bumpUseCount(+1);
          return regKey;
      }