[Rust] Can't validate schema with value when Nullable union has multiple types.

{ "type": "record", "namespace": "datatypes", "name": "nullunion", "fields": [ {"name": "item", "type": [ "null", "long", "double" ] } ] } 

/// Auto-generated type for unnamed Avro union variants.

#[derive(Debug, PartialEq, Clone, serde::Deserialize, serde::Serialize)]
pub enum UnionLongDouble {    Long(i64),    Double(f64),}

#[derive(Debug, PartialEq, Clone, serde::Deserialize, serde::Serialize)]
pub struct NullUnion {    pub item: Option<UnionLongDouble>,}

#[test]
fn test_multivalue_union_tovalue() {
    let nuschema = r#"
    {
        "type": "record",
        "namespace": "datatypes",
        "name": "nullunion",
        "fields":
        [
            {"name": "item",
                "type": [
                    "null",
                    "long",
                    "double"
                ]
            }
        ]
    }
    "#;   

    let nullunion = NullUnion {
        item: Some(UnionLongDouble::Long(34)),
    };    let schema = Schema::parse_str(nuschema).unwrap();    

    let nu_value = to_value(nullunion).unwrap();
    let nu_encoded = to_avro_datum(&schema, nu_value).unwrap();
}