static Lookup from(Function<GroupReference, Stream<PlanNode>> resolver) {
    return node -> {
      checkArgument(
          node instanceof GroupReference,
          "Node '%s' is not a GroupReference",
          node.getClass().getSimpleName());
      return resolver.apply((GroupReference) node);
    };
  }
A Lookup implementation that does not perform lookup. It satisfies contract by rejecting {@link
GroupReference}-s.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/iterative/Lookup.java