docs: public final String getJmsxAppId() {
          int choice = getHdr2().getChoiceField(JsHdr2Access.XAPPID);
          if (choice == JsHdr2Access.IS_XAPPID_EMPTY) {
              return null;
          }
          else if (choice == JsHdr2Access.IS_XAPPID_COMPACT) {
              try {
                  return MfpConstants.JMSXAPPIDS[((Byte) getHdr2().getField(JsHdr2Access.XAPPID_COMPACT)).intValue()];
              } catch (ArrayIndexOutOfBoundsException e) {
                  FFDCFilter.processException(e, "com.ibm.ws.sib.mfp.impl.JsApiHdrsImpl.getJmsxAppId", "1059");
                  return null;
              }
          }
          else {
              return (String) getHdr2().getField(JsHdr2Access.XAPPID_STRINGVALUE);
          }
      }