@Nullable
  private YouTrackIssue fetchIssue(@NotNull String issueId) throws URISyntaxException, IOException {
    URI endpoint = new URIBuilder(getRestApiUrl("api", "issues", issueId))
      .addParameter("fields", YouTrackIssue.DEFAULT_FIELDS)
      .build();
    return getHttpClient().execute(new HttpGet(endpoint),
                                   JsonResponseHandlerBuilder.fromGson(GSON)
                                     .errorHandler(this::parseYouTrackError)
                                     .ignoredCode(code -> code == HttpStatus.SC_NOT_FOUND)
                                     .toSingleObject(YouTrackIssue.class));
  }
@Nullable
  private YouTrackIssue fetchIssue(@NotNull String issueId)