DuckDB queries into structures aren't escaped correctly

I'm trying to find all the items that contain a specific variable name, like "hurs".

The item with the "hurs" variable looks like this:

and I know that WHERE "cube:variables".hurs IS NOT NULL works.

But what should the filter argument for rustac look like?

cql_json_filter = {
    "op": "is_not_null",
    "args": [
        {"property": "cube:variables.hurs"}
    ]
}
items = await rustac.search('stac_items.parquet', filter=cql_json_filter)

doesn't error, but doesn't return my item either.

I pretty sure this is some simple user syntax error, here, right?

Start at the rustac.search filter handling for stac_items.parquet and trace how the CQL JSON property cube:variables.hurs is passed to the DuckDB query. Check the existing filter-related tests or add a focused case for a non-null nested structure property. Done means the query returns the item containing hurs without breaking other structure filters.