code: private User resolveUser(RequestContext requestContext, List<String> emails) {
      User user = null;
      UserEmailDAO userEmailDAO = new UserEmailDAO();
      for (String email : emails) {
        UserEmail userEmail = userEmailDAO.findByAddress(email);
        if (userEmail != null) {
          if (user == null) {
            user = userEmail.getUser();
          }
          else if (!user.getId().equals(userEmail.getUser().getId())) {
            Messages messages = Messages.getInstance();
            Locale locale = requestContext.getRequest().getLocale();
            throw new SmvcRuntimeException(EdelfoiStatusCode.LOGIN_MULTIPLE_ACCOUNTS, messages.getText(locale, "exception.1023.loginMultipleAccounts"));
          }
        }
      }
      return user;
    }
docs: Determines a common <code>User</code> corresponding to the given list of e-mail addresses. If none of the e-mail addresses are in
  use, returns <code>null</code>. If the e-mail addresses are associated to multiple user accounts, an <code>SmvcRuntimeException</code>
  is thrown.
  
  @param requestContext Request context
  @param emails The list of e-mail addresses to validate
  
  @return The common <code>User</code> corresponding to the given list of e-mail addresses, or <code>null</code> if the addresses are
  not in use
  
  @throws SmvcRuntimeException If the e-mail addresses are associated to multiple user accounts