Jackson QName serailization without namesampe/prefix

I'm trying to deserialze a Map using Jackson 2, the default ObjectMapper() gives something like:

{"{http://google.com/}myName":"myValue"}

It probably uses QName.toString() method to serialize the qname key.

I tried following to register a custom serializer for QName, but it is not getting invoked.

public static class QnameSerializer extends JsonSerializer<QName> {
    @Override
    public void serialize(QName value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
        jgen.writeString(value.getLocalPart());
    }
}

public static void main(String[] args) throws JsonProcessingException {
    SimpleModule module = new SimpleModule();
    module.addKeySerializer(QName.class, new QnameSerializer());
    // tried module.addSerializer(QName.class, new QnameSerializer()) also
    ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(module);
    Map<QName, String> m =ImmutableMap.of(new QName("http://google.com/","myName","pre"), "myValue");
    System.out.println(mapper.writeValueAsString(m));
}

Am I missing something?