title: @JSONUnwrapped on the embedded field flattened issue
body: <p>I have class:</p>
  
  <pre><code>public class Person{
  private int id;
  @JsonUnwrapped
  private Father father
  //getters/setters
  
  @ToString
  @Accessors
  public static class Father{
    private String name;
    private String surname;
  }
  </code></pre>
  
  <p>and form following JSON file</p>
  
  <pre><code>{
    "id": 12,
    "name": "Ned",
    "surname": "Stark"
  }
  </code></pre>
  
  <p>while reading:</p>
  
  <pre><code>ObjectMapper mapper = new ObjectMapper();
  Person myPerson =
          mapper.readValue(new File("src/main/resources/data/rest/person.json"), Person.class);
   System.out.println(myPerson);
  </code></pre>
  
  <p>I keep getting:</p>
  
  <pre><code>(...) father=Student.Father(name=null, surname=null)
  </code></pre>
  
  <p>with error:</p>
  
  <blockquote>
    <p>Exception in thread "main"
    com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No
    serializer found for class
    com.example.demo.rest.r01_json.Person$Father and no properties
    discovered to create BeanSerializer (to avoid exception, disable
    SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain:
    com.example.demo.rest.r01_json.Person["father"]</p>
  </blockquote>
  
  <p><strong>What shall I correct to provide the flattened father content? Or it is not possible and  I must put it as an nested JSON object like</strong>?:</p>
  
  <pre><code>"father":{
    "name": "Ned",
    "surname": "Stark"
  }
  </code></pre>
  
  <p>EDIT</p>
  
  <p>I have edited it to add <code>Person</code> cosntructor with </p>
  
  <pre><code> @JsonCreator // DESERIALIZATION: JSON -&gt; POJO
    public Person(
  ...
  
        @JsonProperty("name") String name,
        @JsonProperty("surname") String surname) {
  ...
      this.father = new Father(name, surname);
  </code></pre>
  
  <p>with <code>Father</code> nested within <code>Person</code> class:</p>
  
  <pre><code>@AllArgsConstructor
    private static class Father {
      private String name;
      private String surname;
    } 
  </code></pre>
  
  <p>still getting:</p>
  
  <pre><code>Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.example.demo.rest.r01_json.Person$Father` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
  </code></pre>