Shuffle Strings

using System;
using System.Linq;

internal class ConsoleTests
{

    public static string ShuffleString(string stringToShuffle)
    {
        if (String.IsNullOrEmpty(stringToShuffle))
        {
            throw new ArgumentNullException("stringToShuffle",
                "The stringToShuffle variable must not be null or empty");
        }

        return new string(
            stringToShuffle
                .OrderBy(character => Guid.NewGuid())
                .ToArray()
            );
    }

    public static string ShuffleStringExcludeOriginal(string stringToShuffle)
    {
        string shuffled;

        if (String.IsNullOrEmpty(stringToShuffle))
        {
            throw new ArgumentNullException("stringToShuffle",
                                            "The stringToShuffle variable must not be null or empty");
        }

        if (stringToShuffle.Length < 2)
        {
            throw new ArgumentException("This method can not be used when the string to shuffle is less than two " +
                                        "characters long as it is not possible to exclude the original",
                                        "stringToShuffle");
        }

        do
        {
            shuffled = new string(
                                    stringToShuffle
                                        .OrderBy(character => Guid.NewGuid())
                                        .ToArray()
                                    );
        } while (shuffled == stringToShuffle);

        return shuffled;
    }
}