How can I add simple String value to JsonObjectBuilder?

Question

This is a follow-up question from Java JsonObjectBuilder adding extra 'metadata' when added as child to JsonObjectBuilder.

When I add a String, I see

"href":{
    "chars":"http://test.com/test/1",
    "string":"http://test.com/test/1",
    "valueType":"STRING"
}

What I expected is

"href": "http://..."

When I add a number, I see

"a":{
    "integral":true,
    "valueType":"NUMBER"
}

I expect something like

"a": 1

What did I do wrong?

This is my code.

@Override
public JsonObject adaptToJson(final Link original) throws Exception {
    return ofNullable(original).map(v -> {
        final JsonObjectBuilder builder = createObjectBuilder();
        //builder.add("a", 1);
        //builder.add("b", 1L);
        ofNullable(v.getUri()).map(URI::toString).ifPresent(href -> builder.add("href", JsonbBuilder.create().toJson(href, String.class)));
        ofNullable(v.getRel()).ifPresent(rel -> builder.add("rel", rel));
        ofNullable(v.getTitle()).ifPresent(title -> builder.add("title", title));
        return builder.build();
    }).orElse(null);
}

And I'm using johnzon-jsonb. yasson seems have a problem.