如何在CLR UDF中返回nvarchar(max)？

[return: SqlFacet(MaxSize = -1)]
public static SqlString MyFunction()
{
    // Your code here
}

public static SqlString MyFunction()
{
    string result = "";
    // Your code here
    if (result.Length > 2147483647)
    {
        result = result.Substring(0, 2147483647);
    }
    return result;
}

public static SqlChars MyFunction()
{
    SqlChars result = new SqlChars(new char[0]);
    // Your code here
    return result;
}