code: public List<GitlabUser> findUsers(String emailOrUsername) throws IOException {
          List<GitlabUser> users = new ArrayList<>();
          if (emailOrUsername != null && !emailOrUsername.equals("")) {
              String tailUrl = GitlabUser.URL + "?search=" + emailOrUsername;
              GitlabUser[] response = retrieve().to(tailUrl, GitlabUser[].class);
              users = Arrays.asList(response);
          }
          return users;
      }
docs: Finds users by email address or username.
  
  @param emailOrUsername Some portion of the email address or username
  @return A non-null List of GitlabUser instances.  If the search term is
  null or empty a List with zero GitlabUsers is returned.
  @throws IOException on gitlab api call error