public class TestModel
{
    public string StudentId { get; set; }
}
public class MvcTemplate<T> : RazorEngineTemplateBase<T>
{
    public MyHtmlHelper<T> Html { get; set; }
}
public class MyHtmlHelper<T>
{
    private readonly MvcTemplate<T> templateInstance;
    public MyHtmlHelper(MvcTemplate<T> templateInstance)
    {
        this.templateInstance = templateInstance;
    }
    public string Hidden(Expression<Func<T, object>> selector)
    {
        object propertyValue = selector.Compile()(this.templateInstance.Model);
        MemberExpression body = (MemberExpression)selector.Body;
        string name = HttpUtility.HtmlAttributeEncode(body.Member.Name);
        string value = HttpUtility.HtmlAttributeEncode(propertyValue?.ToString() ?? "");
        return $"<input type=\"hidden\" name=\"{name}\" value=\"{value}\" \\>";
    }
}
class Program
{
    static void Main(string[] args)
    {
        string content = @"
              <p>hidden: @Html.Hidden(m => m.StudentId)</p>                  
          ";
        RazorEngine razorEngine = new RazorEngine();
        var compiledTemplate = razorEngine.Compile<MvcTemplate<TestModel>>(content);
        string result = compiledTemplate.Run(template =>
        {
            template.Model = new TestModel()
            {
                    StudentId = "<script>alert(\"1\");</script>"
            };
            template.Html = new MyHtmlHelper<TestModel>(template);
        });
        Console.WriteLine(result);
        Console.ReadKey();
    }
}