Replace Invalid File Name Characters in C#

/// <summary>
/// Replaces invalid file name characters with '_'
/// </summary>
public static string ReplaceInvalidFileNameChars(string fileName)
{
    var result = new StringBuilder();
    var invalidChars = Path.GetInvalidFileNameChars();

    var current = 0;
    while (current < fileName?.Length)
    {
        var next = fileName.IndexOfAny(invalidChars, current);
        if (next >= 0)
        {
            result.Append(fileName.Substring(current, next - current));
            result.Append('_');
            current = next + 1;
        }
        else
        {
            result.Append(fileName.Substring(current));
            break;
        }
    }

    return result.ToString();
}