Gson serialization - handling missing fields

Question

I am using gson to deserialize/serialize data. Currently I use simple deserialization to just get the json data to pojo representation as is. Next I use custom serialization to parse json output.

I have some problems with nested fields. When the json data has some missing nested field I am unable to access them in the Serialization step, with NullPointerException error. Example - I have an address nested field, which can contains of city, zipcode and so on. If the incoming json has no address field, I got NullPointerException when accerssing address.city.

As a result, if some json field are missing, I just want to populate missing values as output in serrialization, but I would like to add a reasonable null error handling. No obligatory checks are required.

myCustomer pojo example:

import com.google.gson.*;
import org.junit.Test;

import java.lang.reflect.Type;
import java.util.Date;

public class MyGsonTest {

    // my deserialization class
    class MyCustomer {

        // fields
        String id;
        String name;
        Date birthdate;

        // nested fields
        Address address;
        Description description;

        class Address {
            String city;
            String zipCode;
            Street street;

            // nested fields can have multiple in-depth levels, but I have simplified it for the presentation purposes
            class Street {
                String apartment;
                String number;
            }

        }

        class Description {
            String info;
            String moreInfo;
        }

    }

    // my custom deserialization class
    public class MyCustomerSerializer implements JsonSerializer<MyCustomer> {

        @Override
        public JsonElement serialize(MyCustomer myCustomer, Type type, JsonSerializationContext jsonSerializationContext) {

            // create initial/empty JsonObject
            JsonObject jo = new JsonObject();

            // next add some properties...

            // ok - we access created/deserialized nested field
            jo.addProperty("city", myCustomer.address.city);
            jo.addProperty("zipcode", myCustomer.address.zipCode); // ok iven if underlying field is missing

            /*
            !!!
            NullPointerException - deserialized nested field is null (no leaf-level fields)
            !!!
             */
            jo.addProperty("info", myCustomer.description.info);
            jo.addProperty("moreInfo", myCustomer.description.moreInfo);

            return jo;
        }
    }

    @Test
    public void testRun() {

        // create gson instance with gson builder
        GsonBuilder gsonBuilder = new GsonBuilder()
            // register custom deserializer for MyCustomer class
            .registerTypeAdapter(MyCustomer.class, new MyCustomerSerializer());
        Gson gson = gsonBuilder.create();


        // get example data
        // missing: 'city.zipCode' and entire 'description'
        String myCustomer1String = "{'id':'a123','name':'John','birthdate':'1987-01-01','address':{'city':'Colorado'}}";

        // deserialize - create customer pojo instance
        MyCustomer myCustomer = gson.fromJson(myCustomer1String, MyCustomer.class);

        // serialization - error occur here
        String myCustomerParsed = gson.toJson(myCustomer);

    }
}```