docs: public FormValidation doCheckRetryCount(@QueryParameter String value)throws IOException,ServletException{
          // retry count is optional so this is ok
          if(value == null || value.trim().equals(""))
              return FormValidation.ok();
          if (!value.matches("[0-9]*")) {
              return FormValidation.error("Invalid retry count");
          }
          return FormValidation.ok();
      }