LOJ on subquery with UNNEST for array indexes throwing type error

SET               `compiler.arrayindex` "true";

DROP DATAVERSE    TestDataverse IF EXISTS;

CREATE DATAVERSE  TestDataverse;

USE               TestDataverse;

CREATE TYPE       GenericType AS { _id: uuid  };

CREATE DATASET    IndexedDataset (GenericType)

PRIMARY KEY       _id AUTOGENERATED;

CREATE DATASET    ProbeDataset (GenericType)

PRIMARY KEY       _id AUTOGENERATED;

CREATE INDEX      TestIdx

ON                IndexedDataset (

    UNNEST items    

    SELECT val : bigint

);

FROM             ProbeDataset P

LEFT OUTER JOIN  ( 

    FROM IndexedDataset I   

    UNNEST I.items II    

    SELECT VALUE II.val

) AS IIV

ON                IIV /* +indexnl */ = TO_BIGINT(P.val)

SELECT            DISTINCT P;