code: @Override
  	protected void mergeBranchPlanMaps(Map<OptimizerNode, PlanNode> branchPlan1, Map<OptimizerNode,
  			PlanNode> branchPlan2){
  
  	}
docs: Merging can only take place after the solutionSetDelta and nextWorkset PlanNode has been set,
  because they can contain also some of the branching nodes.