Mongodb多态性Java对象无法确定具体类

public abstract class Animal {
    private String type;
    // getters and setters
}

public class Dog extends Animal {
    private String breed;
    // getters and setters
}

public class Cat extends Animal {
    private String color;
    // getters and setters
}

import org.springframework.data.annotation.Id;
import org.springframework.data.annotation.Transient;
import org.springframework.data.mongodb.core.mapping.Document;
import org.springframework.data.mongodb.core.mapping.DiscriminatorKey;
import org.springframework.data.mongodb.core.mapping.DiscriminatorValue;

@Document
@DiscriminatorKey(name = "animalType")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public abstract class Animal {
    @Id
    private String id;
    private String type;
    // getters and setters
}

@Document
@DiscriminatorValue("Dog")
public class Dog extends Animal {
    private String breed;
    // getters and setters
}

@Document
@DiscriminatorValue("Cat")
public class Cat extends Animal {
    private String color;
    // getters and setters
}

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

public class Main {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
        MongoDatabase database = mongoClient.getDatabase("test");
        MongoCollection<Document> collection = database.getCollection("animals");

        Document doc = collection.find(new Document("type", "Dog")).first();
        String animalType = doc.getString("type");
        Animal animal;

        if ("Dog".equals(animalType)) {
            animal = doc.toBsonDocument(BsonDocument.class).toJavaObject(Dog.class);
        } else if ("Cat".equals(animalType)) {
            animal = doc.toBsonDocument(BsonDocument.class).toJavaObject(Cat.class);
        } else {
            throw new IllegalArgumentException("Unknown animal type");
        }

        System.out.println(animal);
    }
}