code: @Override
      public int doStartTag() throws JspException {
  
          if (value == null) {
              timeZone = TimeZone.getTimeZone("GMT");
          } else if (value instanceof String) {
              if (((String) value).trim().equals("")) {
                  timeZone = TimeZone.getTimeZone("GMT");
              } else {
                  timeZone = TimeZone.getTimeZone((String) value);
              }
          } else {
              timeZone = (TimeZone) value;
          }
  
          return EVAL_BODY_BUFFERED;
      }
docs: Tag logic