mongodb - Aggregation.project使用filter筛选时，item为null怎么办？

Question

ProjectionOperation projectionOperation1 = Aggregation.project("uid", "userName", "userAvatar", "action", "objectType", "objectOthers",
                "createdDt", "url_as", "userCopyUrl_as")
                .andExpression("toString(objectId)").as("objectId")
                .andExpression("toString(_id)").as("id")
.and(filter("userLikeUrl_as").as("item")
.by(ComparisonOperators.Eq.valueOf("item.valid").equalToValue(1))).as("userLikeUrl_as_list");

Answer 1

ProjectionOperation projectionOperation1 = Aggregation.project("uid", "userName", "userAvatar", "action", "objectType", "objectOthers",
        "createdDt", "url_as", "userCopyUrl_as")
        .andExpression("toString(objectId)").as("objectId")
        .andExpression("toString(_id)").as("id")
        .and(ConditionalOperators.Cond.when(Criteria.where("userLikeUrl_as.item").ne(null))
                .then(filter("userLikeUrl_as").as("item")
                        .by(ComparisonOperators.Eq.valueOf("item.valid").equalToValue(1)))
                .otherwise(new ArrayList<>()))
        .as("userLikeUrl_as_list");

Answer 2

解决了，是因为返回的对象类型使用的是int，应该使用Integer才行，因为Integer允许为Null

private Long total;
private Integer pageNum;
private Integer pageSize;
private List<HashMap> rows;