Filters.and(
  Filters.not(Filters.eq("foo", new DBRef("1", "1"))),
  Filters.not(Filters.eq("foo.bar", new DBRef("1", "1"))))

This code generates the query:

{ "foo" : { "$not" : { "$ref" : "1", "$id" : "1" } }, "foo.bar" : { "$not" : { "$ref" : "1", "$id" : "1" } } }

Which after that complains with:

com.mongodb.MongoQueryException: Query failed with error code 2 and error message 'unknown operator: $ref' on server localhost:27017

When passed to the DB. Am I missing something or is this a bug?