docs: synchronized final JsMsgPart getPayload(JMFSchema schema) {
          if (payload == null) {
              if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
                  SibTr.debug(this, tc, "getPayload will call getPart");
              payload = jmo.getPayloadPart().getPart(JsPayloadAccess.PAYLOAD_DATA, schema);
          }
          return payload;
      }