JsonMappingException when POST and deserialize to a HashMap

Hi
I'm trying to create a new Document in my MongoDB using the DATA-REST-API but when the json contains data for the HashMap attribute, it fails with JsonMappingException: Can not deserialize instance of java.lang.String out of FIELD_NAME token

Using the default configuration (RepositoryRestMvcConfiguration)

Foo.java

@Document
public class Foo implements Serializable {
      @Id
      private String id;
      private String name;
      private HashMap<String, String> map = new HashMap<String, String>();
      // getters & setters omitted
}

FooRepository.java

public interface FooRepository extends MongoRepository<Foo, String> {}

FooTest.java

@RunWith(SpringJUnit4ClassRunner.class)
@WebAppConfiguration()
@ContextConfiguration()
public class FooTest {
    @Autowired private WebApplicationContext wac;
    @Autowired private FooRepository repo;
    private MockMvc mockMvc;

    @Before
    public void setup() {
        this.mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();
     }

    @Test    
    // It works 
    public void testGET() throws Exception {
         repo.deleteAll();
         HashMap<String, String> map = new HashMap<String,String>();
         map.put("key1", "value1");
         map.put("key2", "value2");
         Foo foo = new Foo(); foo.setName("FooName"); foo.setMap(map);
         Foo saved = repo.save(foo);

         // test GET foo
         MvcResult result = this.mockMvc.perform(get("/foo/" + saved.getId())
          .accept(MediaType.parseMediaType("application/json;charset=UTF-8")))
          .andExpect(status().isOk())
          .andExpect(content().contentType("application/json;charset=UTF-8"))
          .andExpect(jsonPath("$.name").value(foo.getName()));
         String content = result.getResponse().getContentAsString();
         System.out.println( "result /foo/" + saved.getId() + ":\n" + content);

    }

    @Test 
    // It works :-)
    public void testPOST1() throws Exception {
        repo.deleteAll();
        String json = "{\"name\":\"testSimple\"}";
        this.mockMvc.perform(post("/foo")
            .contentType(MediaType.parseMediaType("application/json;charset=UTF-8"))
            .content(json))
            .andExpect(status().is(201));
     }

    @Test 
    // It doesn't work :-( 
    public void testPOST2() throws Exception {
        repo.deleteAll();
        String json = "{\"name\":\"test\", \"map\":{\"key1\":\"value1\", \"key2\":\"value2\"}}"; 
       this.mockMvc.perform(post("/foo")
            .contentType(MediaType.parseMediaType("application/json;charset=UTF-8"))
            .content(json))
            .andExpect(status().is(201));
       }
}

Start with FooTest.java, especially testPOST2, and reproduce the POST through MockMvc using RepositoryRestMvcConfiguration; compare it with testPOST1 and the repository-backed GET. Trace the request into the map field in Foo.java and FooRepository.java, then confirm the nested HashMap JSON POST returns 201 and preserves both entries.