But, it is easy to find such a shape, you could track back the steps.
1. Open drawing explorer.
2. Unlock the protection by right click on the drawing name.
3. Show the handle of the shape by right click on the shape, sheet.40.
4. Show the shapesheet by selecting the menu to show the shaped\sheet.
5. Find the cells that makes the shape unseen, and unlock them.
Please note that a white line and white paint are also unseen.