code: public List<GitlabProjectMember> getNamespaceMembers(Integer namespaceId) throws IOException {
          String tailUrl = GitlabGroup.URL + "/" + namespaceId + GitlabProjectMember.URL;
          return Arrays.asList(retrieve().to(tailUrl, GitlabProjectMember[].class));
      }
docs: This will fail, if the given namespace is a user and not a group
  
  @param namespaceId Namespace ID
  @return A list of Gitlab Project members
  @throws IOException on gitlab api call error