ADO.NET: Send procedure parameter with null value

I need to send a parameter a null value to the procedure, but I get an error: System.Data.SqlClient.SqlException: ‘Procedure or function ‘sel_mizanyeni’ expects parameter ‘@subeno’, which was not supplied.’ When I run the same procedure with the same parameters in SQL Server, it does not cause an error. When I run it with ADO.NET in C#, I get that error. […]