JSNI return types with CellTable

DataDictJSOexample.java

public class DataDictJSO extends JavaScriptObject {
...
    public final native void put(String key, String obj) /*-{
        this[key] = obj;
    }-*/;

    /**
     * A slick way to get down to the object.
     * @param keys can be "foo" or "foo.bar.baz"
     * @param <T>
     * @return
     */
    public final native <T> T get(String keys) /*-{
        var val = this;
        var keys = keys.split(".");
        for (var ii=0; ii<keys.length; ii++) {
            var key = keys[ii];
            val = val[key];
        }
        return val;
    }-*/;
}

public class DictColumn<K>
        extends Column<DataDictJSO, K> {
    String key;
    
    public DictColumn(Cell cell, String fieldKey) {
        super(cell);
        this.key = fieldKey;
    }

    @Override
    public K getValue(DataDictJSO object) {
        return object.<K>get(key);
    }
}

...
        cellTable.addColumn(new DictColumn<String>(new EditTextCell(), "name"), "Name");
        cellTable.addColumn(new DictColumn<Boolean>(new CheckboxCell(), "is_a.administrator"), "Administrator");
        ListDataProvider<DataDictJSO> provider = new ListDataProvider<DataDictJSO>();
        provider.addDataDisplay(cellTable);

        String data = "[{\"id\":\"admin\",\"password_sha\":\"ddf32cd4eb1caa4260d0ab626b2b3f1f7dec4a8c\",\"name\":\"Administrator\",\"is_a\":{\"administrator\":true}}]";
        JSONArray users = (JSONArray) JSONParser.parseLenient(data);
        List<DataDictJSO> list = provider.getList();
        for (int ii = 0; ii<users.size(); ii++) {
            list.add((DataDictJSO) ((JSONObject) users.get(ii)).getJavaScriptObject());
        }