code: public OQuery<T> setFetchPlan(final String fetchPlan) {
      OFetchHelper.checkFetchPlanValid(fetchPlan);
      if (fetchPlan != null && fetchPlan.length() == 0)
        this.fetchPlan = null;
      else
        this.fetchPlan = fetchPlan;
      return this;
    }
docs: Sets the fetch plan to use.