HateOas 가 업데이트가 되어서, "Spring HATEOAS" 코드를 아래처럼 하셔야 될겁니다.

package hello.hateoas;

import org.springframework.hateoas.RepresentationModel;

public class Hello extends RepresentationModel<Hello> {
    private String prefix;
    private String name;

    public String getPrefix() {
        return prefix;
    }

    public void setPrefix(String prefix) {
        this.prefix = prefix;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return prefix + name;
    }
}

package hello.hateoas;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;


import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.linkTo;
import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.methodOn;


@RestController
public class SampleController  {


    @GetMapping("hello")
    public Hello hello() {
        Hello hello = new Hello();
        hello.setPrefix("Hey.");
        hello.setName("keesun");
        hello.add(linkTo(methodOn(SampleController.class).hello()).withSelfRel());


        return hello;
    }
}

Test Code 는 동일 합니다.