code: final JsMsgMap getSystemContextMap() {
          if (systemContextMap == null) {
              List<String> keys = (List<String>) getApi().getField(JsApiAccess.SYSTEMCONTEXT_NAME);
              List<Object> values = (List<Object>) getApi().getField(JsApiAccess.SYSTEMCONTEXT_VALUE);
              systemContextMap = new JsMsgMap(keys, values);
          }
          return systemContextMap;
      }
docs: Helper method used by the System Context methods to obtain the
  System Context items in the form of a map.
  <p>
  The method has package level visibility as it is used by
  MQJsJmsMessageEncoderImpl.
  
  @return A JsMsgMap containing the Message Property name-value pairs.