我正在Spring应用程序中使用mongodb进行以下搜索：

import org.bson.Document;
import org.bson.types.ObjectId;
import org.springframework.data.mongodb.core.FindAndModifyOptions;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.core.query.Update;

private CampaignEntity incrByWithConversionRate(ObjectId campaignId, String key) {
    Query query = new Query();
    query.addCriteria(Criteria.where("id").is(campaignId));

    Update update = new Update();
    update.inc(key);
    update.set("conversionRate", new Document("$divide", Arrays.asList("$clicks", "$views")));

    return mongoTemplate.findAndModify(
        query, update,
        new FindAndModifyOptions().returnNew(true), CampaignEntity.class);
}

问题是它失败并出现以下错误：

org.springframework.data.mapping.MappingException: Expected to read Document Document{{$divide=[$clicks, $views]}} into type class java.lang.Float but didn't find a PersistentEntity for the latter!

注：CampaignEntity类定义如下：

@Data
@Document(collection = "campaigns")
public abstract class CampaignEntity extends BaseEntity {
    private Integer clicks = 0;
    private Integer views = 0;
    private Float conversionRate;
}