Function map_property_value 

pub fn map_property_value(val: &Value, prop: &str) -> Value

Extract a named property from a runtime map/struct value. Returns Value::Null when val is not a map/struct or the key is absent.

Used to resolve property access on a variable bound to a map/struct column, e.g. UNWIND $rows AS row CREATE (:Memory {id: row.id}) (P53.26).