public class Student {
    private Integer x = Integer.valueOf(1000);

    public Integer getX() {
        return x;
    }

    public void setX(Integer x) {
        if(x != null) {
           this.x = x;
        }
    }
}

This works for me........

Test code 1:

public static void main(String[] args) throws IOException {
        String s = "{\"x\":null}";
        ObjectMapper mapper = new ObjectMapper();
        Student ss = mapper.readValue(s, Student.class);
        System.out.println(ss.getX());
    }

output:

1000

Test code 2:

public static void main(String[] args) throws IOException {
        String s = "{}";
        ObjectMapper mapper = new ObjectMapper();
        Student ss = mapper.readValue(s, Student.class);
        System.out.println(ss.getX());
    }

output:

1000

Another way to get the inner element, with .at() method:

rootNode.at("/HotelListResponse/customerSessionId")

You need to use an ObjectMapper:

ObjectMapper mapper = new ObjectMapper();
JsonFactory factory = mapper.getJsonFactory(); // since 2.1 use mapper.getFactory() instead
JsonParser jp = factory.createJsonParser("{\"k1\":\"v1\"}");
JsonNode actualObj = mapper.readTree(jp);

Further documentation about creating parsers can be found here.