public class Test{
	public static void main(String[] args) throws JsonProcessingException {
		People people = new People();
		people.setName(null);
		people.setEmail("email");

		ObjectMapper objectMapper = new ObjectMapper();
		String json = objectMapper.writeValueAsString(people);

		System.out.println(json);
	}
}

@Setter
@NoArgsConstructor
@JsonInclude(Include.NON_EMPTY) // null이 아닌 것만 직렬화/역직렬화가 가능하도록 조건을 검
class People{
	private String name;
	private String email;
}

{"email":"email"}