Problem with `@JsonTypeInfo.As.EXTERNAL_PROPERTY`, `defaultImpl`, missing type id, NPE

[cowtowncoder]

(as reported by Joe O on mailing list)

---

Looks like one of following test methods fails:

public class JsonTypeInfoTest extends BaseMapTest
{
    public enum Attacks { KICK, PUNCH }

    static class Character {
        public String name;
        public Attacks preferredAttack;

        @JsonTypeInfo(use=JsonTypeInfo.Id.NAME, defaultImpl=Kick.class,
                include=JsonTypeInfo.As.EXTERNAL_PROPERTY, property="preferredAttack")
        @JsonSubTypes({
            @JsonSubTypes.Type(value=Kick.class, name="KICK"),
            @JsonSubTypes.Type(value=Punch.class, name="PUNCH")
        })
        public Attack attack;
    }

    public static abstract class Attack {
        public String side;

        @JsonCreator
        public Attack(String side) {
            this.side = side;
        }
    }

    public static class Kick extends Attack {
      @JsonCreator
      public Kick(String side) {
        super(side);
      }
    }

    public static class Punch extends Attack {
      @JsonCreator
      public Punch(String side) {
        super(side);
      }
    }

    final ObjectMapper MAPPER = new ObjectMapper();

    public void testFails() throws Exception {
      String json = "{ \"name\": \"foo\", \"attack\":\"right\" } }";

      Character character = MAPPER.readValue(json, Character.class);

      assertNotNull(character);
      assertNotNull(character.attack);
      assertEquals("foo", character.name);
    }

    public void testWorks() throws Exception {
      String json = "{ \"name\": \"foo\", \"preferredAttack\": \"KICK\", \"attack\":\"right\" } }";

      Character character = MAPPER.readValue(json, Character.class);

      assertNotNull(character);
      assertNotNull(character.attack);
      assertEquals("foo", character.name);
    }
  }

with a NullPointerException (with 2.7.3, current master)

[cowtowncoder]

Ok, so the underlying issue is related to couple of things; and combination of missing type id (needing to use defaultImpl), along with special handling of "natural" types (of which String, used here as JSON value to bind is one) results in trouble. null specifically just refers to missing Map for resolving Class to "type id" (since it's not usually needed for deserialization, only serialization).
But it probably goes deeper than that. Will keep digging.

[cowtowncoder]

Managed to fix this so that tests pass. Fix will be in 2.7.4.

[joeo73]

Thanks. In the short term, can you recommend a work around?

[cowtowncoder]

@joeo73 unfortunately the only thing I can think of would be ensuring that the type id is not missing.