public ActionResult IndentXml(IndentXmlArgs args = null)
{
    if (args == null)
        return View(new IndentXmlArgs());

    if (string.IsNullOrEmpty(args.Xml))
        return View(args);

    var indentedXml = IndentXml(args.Xml);
    args.Xml = indentedXml;

    return View(args);
}

/* // here's the view, in case that matters
@model fdumont.Models.IndentXmlArgs

@using (Html.BeginForm("IndentXml", "Utilities", FormMethod.Post, new {@class = "form-horizontal"}))
{
    @Html.TextAreaFor(model => model.Xml, 20, 80, new {style = "font-family: monospace", @class = "span12"})
    <input type="submit" value="submit" class="btn" />
}
*/