SQL: Wrong NULL folding of expression

[matriv]

SELECT POSITION('x',LCASE("first_name")) pos, "first_name" FROM "test_emp"
WHERE POSITION('x',LCASE("first_name")) != 0 OR POSITION('x',LCASE("first_name")) IS NULL;

is translated to:

"InternalSqlScriptUtils.nullSafeFilter(InternalSqlScriptUtils.neq(InternalSqlScriptUtils.position(params.v0,InternalSqlScriptUtils.lcase(InternalSqlScriptUtils.docValue(doc,params.v1))),params.v2))"

The right part of the OR is missing because it's wrongly folded by the FoldNull rule. The POSITION can potentially be null.

[elasticmachine]

Pinging @elastic/es-search-aggs

[costin]

Likely the nullability of the right side is reported incorrectly. IS NULL is not nullable which should cause OR to not be nullable.
As a separate side, due to the 3VL, both OR and AND need to take into account their folding - if it's possible, then they are not nullable (one side is true for OR or one is false for AND).

[matriv]

Yep, also functions like POSITION can have any of their arguments NULL so they are nullable->true if at least one of their children is nullable, I think the logic currently is inversed: nullable->false if any of the children is not nullable