In the SqlMapper.Async [Line 451](https://github.com/DapperLib/Dapper/blob/main/Dapper/SqlMapper.Async.cs#L451) and [Line 1323](https://github.com/DapperLib/Dapper/blob/main/Dapper/SqlMapper.Async.cs#L1323) what is the purpose of calling `Nullable.GetUnderlyingType`, if it is not used afterwards?