private void ValidateExtension()
{
var extension = Path.GetExtension(_filename);
var filenameWithoutExtension = Path.GetFileNameWithoutExtension(_filename);
_validator.Ensure<InvalidPathException>(!filenameWithoutExtension.IsEmpty() || !extension.IsEmpty(), "The filename of the path '{0}' is empty.");
_validator.Ensure<InvalidPathException>(filenameWithoutExtension.IsEmpty() || !Char.IsWhiteSpace(filenameWithoutExtension.Last()), "The filename of the path '{0}' ends with a whitespace which is not allowed.");
}