public Result<Issue> assign(String issueKey, @Nullable String assignee) {
   Result<Issue> result = Result.of();
   try {
     result.set(
         issueService.assign(
             issueKey, StringUtils.defaultIfBlank(assignee, null), UserSession.get()));
   } catch (Exception e) {
     result.addError(e.getMessage());
   }
   return result;
 }