Representing strings with all their characters visible

MakeStringVisible.cs

/// <summary>
/// Returns a visible version of the string, by making
/// its whitespace and control characters visible
/// using well known escape sequences, or the equivalant 
/// hexa decimal value.
/// </summary>
/// <param name="str">The string to be made visible.</param>
/// <returns></returns>
public static string MakeStringVisible(string str)
{
    if (str == null)
        return "{null}";

    StringBuilder sb = new StringBuilder();

    foreach (char ch in str)
    {
        if (Char.IsControl(ch) || Char.IsWhiteSpace(ch))
        {
            switch (ch)
            {
                case '\a':
                    sb.Append("\\a");
                    break;
                case ' ':
                    sb.Append("\\s");
                    break;
                case '\n':
                    sb.Append("\\n");
                    break;
                case '\r':
                    sb.Append("\\r");
                    break;
                case '\t':
                    sb.Append("\\t");
                    break;
                case '\v':
                    sb.Append("\\v");
                    break;
                case '\f':
                    sb.Append("\\f");
                    break;
                default:
                    sb.AppendFormat("\\u{0:X};", (int)ch);
                    break;
            }
        }
        else
        {
            sb.Append(ch);
        }
    }

    return sb.ToString();
}