error[E0277]: the trait bound `<Col as Expression>::SqlType: NotNull` is not satisfied
  --> $DIR/issue-38821.rs:23:17
   |
LL | #[derive(Debug, Copy, Clone)]
   |                 ^^^^ the trait `NotNull` is not implemented for `<Col as Expression>::SqlType`
   |
   = note: required because of the requirements on the impl of `IntoNullable` for `<Col as Expression>::SqlType`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.