Look at the lines
Guid pin = Guid.Empty;
Guid pin1 = ac.FindPen(pin)
Firstly you have a spelling error in there, but importantly you are passing
Guid.Empty
into your FindPin method.
Within that method you only try to look something up
if (pin == null)
Well it's not null, it's Guid.Empty!
Try
if (pin == Guid.Empty)