Function from_empty_relation 

pub fn from_empty_relation(
    producer: &mut impl SubstraitProducer,
    e: &EmptyRelation,
) -> Result<Box<Rel>, DataFusionError>

Encodes an EmptyRelation as a Substrait VirtualTable.

EmptyRelation represents a relation with no input data. When produce_one_row is true, it generates a single row with all fields set to their default values (typically NULL). This is used for queries without a FROM clause, such as “SELECT 1 AS one” or “SELECT current_timestamp()”.

When produce_one_row is false, it represents a truly empty relation with no rows, used in optimizations or as a placeholder.