public AbsoluteFolderPath GetSiblingFolderPath(string folderName)
{
NameHelper.EnsureValidFilenameCharacters(folderName);
// cant from root, can elsewhere
if (Parts.Count == 1)
{
throw PathExceptions.UndefinedSiblingFor(RootValue);
}
var parts = Parts.CloneSublist(Parts.Count - 1);
parts.Add(folderName);
return(new AbsoluteFolderPath(parts));
}