In the development process, it is often necessary to convert the entity class object into a Json string. If it is directly stored as a value in the library, it will be found that the uncopied properties are displayed as null. Here you need to filter out the attribute values that are not copied, and only display the attributes with values.
The packages and annotations introduced by the following entity classes only need one line of annotations.
import com.fasterxml.jackson.annotation.JsonInclude;
@JsonInclude(JsonInclude.Include.NON_NULL)
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