Normal. Tonsils commonly have crypts in them. They are often not symmetric. The hole can often get a white gelatinous gook in them as well.
Can occur. As you grow older, the tonsillar tissue slowly degenerates. As it does it can develop "holes" or crypts. They can seem concerning but not to worry. They can occur only in one or both. However, some patients repeatedly get food trapped in them which leads to white clusters in their tonsils and get lead intractable bad breath. If this happens you might want see an ENT for a possible solution.