code: public List<GitlabLabel> getLabels(Serializable projectId)
              throws IOException {
          String tailUrl = GitlabProject.URL + "/" + sanitizeProjectId(projectId) + GitlabLabel.URL;
          GitlabLabel[] labels = retrieve().to(tailUrl, GitlabLabel[].class);
          return Arrays.asList(labels);
      }
docs: Gets labels associated with a project.
  
  @param projectId The ID of the project.
  @return A non-null list of labels.
  @throws IOException on gitlab api call error