How to add the URL to Smart Search results

Hi

I have been following the example for Smart Search on Github

The SearchResultItem has a field for Url.

Using the example SearchService

var searchItem = new SearchResultItem<BaseInfo>
{
    Fields = new SearchFields
    {
        Title = row["title"].ToString(),
        Content = row["content"].ToString(),
        ImagePath = GetImagePath(objectType, id, row["image"].ToString()),
        Date = date,
        ObjectType = objectType
    },
    Data = GetDataObject(id, objectType)
};

I can readily see the Title etc being extracted from row["Title"] etc.

I can not see how to get the url from the DataRow so that I can create a hyperlink to the page.

I have tried using

    ValidationHelper.GetString(SearchContext.GetSearchValue(id, SearchFieldsConstants.CUSTOM_URL), "#")

but this only returns the default value.

Would somebody please point me to the documentation or in the right direction?

Thanks

Tim