code: public static void setCurrentTraceId(String id) {
      if (id == null) {
        traceId.remove();
      } else {
        traceId.set(id);
      }
    }
docs: Set the Trace ID associated with any logging done by the current thread.
  
  @param id The traceID, in the form projects/[PROJECT_ID]/traces/[TRACE_ID]