code: public static String serializeNativeFlowContext() {
          final FlowContext flowCntext = FLOW_CONTEXT_THREAD_LOCAL.get();
          if (flowCntext != null) {
              return ((FlowContextImpl) flowCntext).serializeNativeFlowContext();
          }
          return "";
      }
docs: Serialize flowContext into a String.
  
  @return String that represent the value of the flowContext in the ThreadLocal.
  if the ThreadscLocal is empty, return empty String "".