我已经浏览了链接：https://jira.spring.io/browse/DATAMONGO-1107，而且我在 * application.properties * 文件中没有看到设置spring.data.mongodb.persist-null-fields=true选项。
Spring Data Mongo甚至不持久化一个空值的字段。如果我想保存空值，如何允许保存？
Person.java

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
@Document
public class Person {
    private String id;
    private String firstName;
    private String lastName;
    private String emailId;
    @Field
    private List<Hobbies> hobbies;
}

Hobbies.java

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Hobbies {
    private String interest;
    private String sports;
}

保存（）-此方法不保存数据。

private void savePersons() {
        Hobbies hobbies1 = Hobbies.builder().interest("Indoor").sports("Chess").build();
        Hobbies hobbies2 = Hobbies.builder().interest("Loveoor").sports("Table Tennis").build();
        Hobbies hobbies3 = Hobbies.builder().interest("Gamedoor").sports("Cricket").build();
        Hobbies hobbies4 = Hobbies.builder().interest("Happydoor").sports("Lawn Tennis").build();

        Person john = Person.builder().firstName("John")
                .emailId("john.kerr@gmail.com").hobbies(Arrays.asList(hobbies1, hobbies2)).build();

        Person neha = Person.builder().firstName("Neha").lastName("Parate")
                .emailId("john.kerr@gmail.com").hobbies(Arrays.asList(hobbies1, hobbies2, hobbies4)).build();

        repository.saveAll(Arrays.asList(john, neha));
    }

• 我没有看到lastName已保存在文档中。* 还有，如何将日期保存为空值？