i followed the tutorial in this answer to make the hemisphere. but when i added it to unity and generated the colliders , the BASE of the sphere had a collider on it. (imagine if hemisphere had like a cover under it). i want the collider to just cover the thickness of the walls of the hemisphere , not the bottom of the sphere.
 i just want to add that when importing it to unity and enabling to generate collision, it doesn't worth either, i have to enable the convex option for it to work.