PreviewWidget.add_widget( widget ) throws "Error: expected an exported object"

[matthew]

Calls to add_widget on expandable PreviewWidgets throws "Error: expected an exported object" (v8-cpp/src/convert.h line: 521) for every widget passed as an argument.

Code:
    var ingredients = new scopes.lib.PreviewWidget("ingredients", "expandable");
    ingredients.add_attribute_value("title", "Ingredients");
    ingredients.add_attribute_value("collapsed-widgets", 0);

    try
    {
        for (var i in ingredientsList)
        {
            var temp = new scopes.lib.PreviewWidget("temp", "text");
            temp.add_attribute_value("text", ingredientsList[i]);

            ingredients.add_widget (temp);
         }
     }
     catch (e)
     {
         console.log(e.name);
         console.log(e.message);
         console.log(e.stack);
     }

Result:
    Error
    expected an exported object
    Error: expected an exported object
        at Error (native)
        at null.<anonymous> (/home/build-my-scope-Ubuntu_SDK_Desktop_Kit-Default/src/my-scope.my-user-id_my-scope.js:203:57)