How to return an nvarchar(max) in a CLR UDF?

/// <summary>
/// Replaces each occurrence of sPattern in sInput with sReplace. This is done with the
/// CLR: new RegEx(sPattern, RegexOptions.Multiline).Replace(sInput, sReplace). The result of the replacement is
/// the return value.
/// </summary>
[SqlFunction(IsDeterministic = true)]
public static  SqlString FRegexReplace(string sInput, string sPattern, string sReplace)
{
    return new Regex(sPattern, RegexOptions.Multiline).Replace(sInput, sReplace);
}

/// <summary>
/// Replaces each occurrence of sPattern in sInput with sReplace. This is done with the
/// CLR: new RegEx(sPattern, RegexOptions.Multiline).Replace(sInput, sReplace). The result of the replacement is
/// the return value.
/// </summary>
[SqlFunction(IsDeterministic = true)]
[return: SqlFacet(MaxSize = -1)]
public static  SqlString FRegexReplace([SqlFacet(MaxSize = -1)]string sInput, string sPattern, string sReplace)
{
    return new Regex(sPattern, RegexOptions.Multiline).Replace(sInput, sReplace);
}