What is the expiation for someone who swore to another person by saying, "The oath is upon me" (علي اليمين), while angry with them for not giving him a paper he requested?

We understand that you swore an oath to someone by saying, "I swear by God you will give me this paper," but he did not. This is not a legally binding oath (yamin shar'iyyah), and breaking it does not necessitate expiation (kaffarah). You must repent to Allah for it.