presto-main/src/main/java/io/prestosql/sql/planner/plan/ProjectNode.java/ProjectNode/ProjectNode
class ProjectNode:    @JsonCreator
    public ProjectNode(@JsonProperty("id") PlanNodeId id,
            @JsonProperty("source") PlanNode source,
            @JsonProperty("assignments") Assignments assignments)
    {
        super(id);

        requireNonNull(source, "source is null");
        requireNonNull(assignments, "assignments is null");

        this.source = source;
        this.assignments = assignments;
    }