presto-main/src/main/java/io/prestosql/execution/NodeTaskMap.java/NodeTaskMap/createOrGetNodeTasks
class NodeTaskMap:    private NodeTasks createOrGetNodeTasks(InternalNode node)
    {
        NodeTasks nodeTasks = nodeTasksMap.get(node);
        if (nodeTasks == null) {
            nodeTasks = addNodeTask(node);
        }
        return nodeTasks;
    }