code: public JenkinsServer createFolder(FolderJob folder, String jobName, Boolean crumbFlag) throws IOException {
          // https://gist.github.com/stuart-warren/7786892 was slightly helpful
          // here
          //TODO: JDK9+: Map.of(...)
          Map<String, String> params = new HashMap<>();
          params.put("mode", "com.cloudbees.hudson.plugins.folder.Folder");
          params.put("name", jobName);
          params.put("from", "");
          params.put("Submit", "OK");
          client.post_form(UrlUtils.toBaseUrl(folder) + "createItem?", params, crumbFlag);
          return this;
      }
docs: Create a job on the server (in the given folder)
  
  @param folder {@link FolderJob}
  @param jobName name of the job.
  @param crumbFlag <code>true</code> to add <b>crumbIssuer</b>
  <code>false</code> otherwise.
  @throws IOException in case of an error.