legacyNull=false forceClassicEngine => count: 2
legacyNull=false trySbeRestricted => count: 3
legacyNull=true forceClassicEngine => count: 2
legacyNull=true trySbeRestricted => count: 2

const docs = [{}, {b: [[], {a: 0}]}, {}];
const pipeline = [{$match: {"b.a": {$gte: null}}}, {$group: {_id: null, n: {$sum: 1}}}];
function count(coll) {
    const res = coll.aggregate(pipeline).toArray();
    return res.length ? res[0].n : 0;
}
for (const knob of [false, true]) {
    db.adminCommand({setParameter: 1, internalQueryLegacyDottedPathNullSemantics: knob});
    for (const eng of ["forceClassicEngine", "trySbeRestricted"]) {
        db.adminCommand({setParameter: 1, internalQueryFrameworkControl: eng});
        db.c.drop();
        docs.forEach((d) => db.c.insertOne(d));
        print("legacyNull=" + knob, eng, "=> count:", count(db.c));
    }
}