Unable to deserialize a null property into a JsonObject

Repro:

import com.google.gson.Gson;
import com.google.gson.JsonObject;

public class GsonDeserialization {

    public static void main(String... args) {
        final Gson gson = new Gson();
        // succeeds
        final MyObject mo1 = gson.fromJson("{ \"name\": null, \"otherProperties\": {} }", MyObject.class);
        // throws
        final MyObject mo2 = gson.fromJson("{ \"name\": \"Alex\", \"otherProperties\": null }", MyObject.class);
    }

    public static class MyObject {
        public String name;
        public JsonObject otherProperties;
    }
}

Exception in thread "main" com.google.gson.JsonSyntaxException: Expected a com.google.gson.JsonObject but was com.google.gson.JsonNull
	at com.google.gson.internal.bind.TypeAdapters$35$1.read(TypeAdapters.java:896)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:129)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:220)
	at com.google.gson.Gson.fromJson(Gson.java:888)
	at com.google.gson.Gson.fromJson(Gson.java:853)
	at com.google.gson.Gson.fromJson(Gson.java:802)
	at com.google.gson.Gson.fromJson(Gson.java:774)
	at com.andrew.scratch.GsonDeserialization.main(GsonDeserialization.java:13)

I would expect the second example to deserialize into an object with a (java) null otherProperties member, but instead it throws a JsonSyntaxException.

[lyubomyr-shaydariv]

@Marcono1234 maybe, but I’m not 100% confident about that and perhaps there should be a comment from the core team to get their design choice and insight first. I just think that having that described in the documentation would tell how to use it properly (prefer JsonElement over JsonObject is there can be nulls) and how to deal with “real” nulls (no property in the JSON document, so the holder can be null and not JsonNull.INSTANCE as expected + explaining that it can be fixed with a custom post-processing interceptor and why applying such an interceptor may cost a little performance) regardless how cumbersome it might be.

This issue is really interesting anyway. 😃

[Marcono1234]

The more I think of this issue, the more I like the idea of just putting this pitfall into the documentation only.

Putting it in the documentation is a good idea either way! Do you want to create a pull request?