Copy character from the string in C#

NKJFK-GPHP7
this can change
????? - ?????
I want to copy like this

string test = TakePieceFromText("this is my data to work with", 2, 5);

/// <summary>
/// Takes the piece from text.
/// </summary>
/// <param name="text">The text.</param>
/// <param name="startIndex">The start index.</param>
/// <param name="length">The length.</param>
/// <returns>a piece of text</returns>
private string TakePieceFromText(string text, int startIndex, int length)
{
    if (string.IsNullOrEmpty(text))
        throw new ArgumentNullException("?????-?????");

    string result = string.Empty;
    try
    {
        result = text.Substring(startIndex, length);
    }
    catch (Exception ex)
    { 
     // log exception
    }
    return result;
}