PouchDB find error: selector containing [null] didn't work properly

[SourceR85]

it("should not match", async () => {
  const db = context.db;

  await db.put({ _id: '1', field: "a" });

  const resp = await db.find({
    selector: { field: [null] }
  });

  resp.docs.should.have.length(0);
});

Response unexpectedly contain documents:

     AssertionError: expected [ Array(1) ] to have a length of 0 but got 1

With CouchDB 3.1.2 (same used in GH CI workflows):

# database connection
db=http://admin:password@localhost:5984/test

# write document
curl -s -H "Content-Type: application/json" -X PUT $db/1 -d '{"field":"a"}' | jq .

# query database
curl -s -H "Content-Type: application/json" -X POST $db/_find -d '{"selector":{ "field":[null] }}' | jq .

Output:

{
  "ok": true,
  "id": "1",
  "rev": "1-3430e46f86eeba0abfef2b577225476a"
}
{
  "docs": [],
  "bookmark": "nil",
  "warning": "No matching index found, create an index to optimize query time."
}