/// <summary>
/// Adds a sequence of Css classes to a <see cref="UserControl"/> if it is not specified.
/// </summary>
/// <param name="control">The control to check.</param>
/// <param name="cssClasses">Sequence of Css classes to add.</param>
/// <exception cref="ArgumentNullException">thrown if <paramref name="cssClasses"/> is <c>Null</c> or <c>Empty</c>.</exception>
public static void AddCssClasses(this UserControl control, params string[] cssClasses)
{
if (cssClasses.IsNullOrEmpty())
{
throw new ArgumentNullException("cssClasses");
}
cssClasses.Distinct().ForEachAsParallel(cssClass => control.AddCssClass(cssClass));
}