ERROR wrong varnullingrels (b 3) (expected (b)) with LEFT JOIN LATERAL and CTE

Hello,

My query has been working fine in 16.4 and before, but not anymore in 16.5,
16.6 and 17. It is a query with multiple CTE, some of which are using
values of the previous ones, and the end of the query sort of make a mix of
found values with aggregation from a LATERAL JOIN. Something like this :

WITH
taxrules AS (...)
, defaultprices AS (...)
, baseprices AS (...)
, currentprices AS (...)
, discountedprices AS (...)

SELECT
discountedprices.variants_id,
discountedprices.products_id,
sum(COALESCE(taxes.tax_price, 0))

FROM
discountedprices
LEFT JOIN LATERAL (
    SELECT
    products_taxrules.products_id,
    round(discountedprices.price * taxrules.rate_percent, 4) -
discountedprices.price AS tax_price
    FROM taxrules
    INNER JOIN products_taxrules ON taxrules.id =
products_taxrules.taxrules_id
) AS taxes ON taxes.products_id = discountedprices.products_id
WHERE
discountedprices.variants_id = ANY(ARRAY[12345])
GROUP BY
discountedprices.variants_id,
discountedprices.products_id,
discountedprices.price
;

I get this error in PG16.5, 16.6 and 17 :
wrong varnullingrels (b 3) (expected (b)) for Var 1/19

The query works again if I add a COALESCE on the line in the LATERAL JOIN
query like this :
round(discountedprices.price * COALESCE(taxrules.rate_percent, 0), 4) -
discountedprices.price AS tax_price

The query also works if I use an INNER JOIN LATERAL instead of a LEFT JOIN
LATERAL.

But the taxrules.rate_percent cannot be null anyway. It comes from the
result of this calculation : (1 + t.rate_percent / 100) AS rate_percent in
the taxrules CTE.

So now I wonder if my sql was wrong and should be fixed or if since 16.5
Postgresql has a bug in the way it deals with values in a LEFT JOIN LATERAL
?

Thanks for your help,

Bertrand Mansion
Mamasam