I would like to use Razor's feature not to produce attribute output inside a tag in case when attribute's value is null. So when Razor meets <div class="@var"> where @var is null, the output will be mere <div>. I've created some Html extension method to write text inside tag. The method takes header text, level (h1..h6), and html attributes as simple object. The code is:

public static MvcHtmlString WriteHeader(this HtmlHelper html, string s, int? hLevel = 1, object htmlAttributes = null)
{
    if ((hLevel == null) || 
        (hLevel < 1 || hLevel > 4) ||
        (s.IsNullOrWhiteSpace()))
        return new MvcHtmlString("");

    string cssClass = null, cssId = null, cssStyle = null;

    if (htmlAttributes != null)
    {
        var T = htmlAttributes.GetType();

        var propInfo = T.GetProperty("class");
        var o = propInfo.GetValue(htmlAttributes);
        cssClass = o.ToString().IsNullOrWhiteSpace() ? null : o.ToString();

        propInfo = T.GetProperty("id");
        o = propInfo.GetValue(htmlAttributes);
        cssId = o.ToString().IsNullOrWhiteSpace() ? null : o.ToString();

        propInfo = T.GetProperty("style");
        o = propInfo.GetValue(htmlAttributes);
        cssStyle = o.ToString().IsNullOrWhiteSpace() ? null : o.ToString();
    }

    var hTag = new TagBuilder("h" + hLevel);

    hTag.MergeAttribute("id", cssId);
    hTag.MergeAttribute("class", cssClass);
    hTag.MergeAttribute("style", cssStyle);
    hTag.InnerHtml = s;

    return new MvcHtmlString(hTag.ToString());
}

I found that in spite of null values for "class" and "style" attributes TagBuilder still puts them as empty strings, like <h1 class="" style=""> But for id attribute it surprisingly works, so when id's value is null, there is no id attribute in tag.

My question - is such behavior something that should actually happen? How can I achieve absent attributes with null values using TagBuilder?

I tried this in VS2013, MVC 5.