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 for `<Col as Expression>::SqlType` to implement `IntoNullable`
  --> $DIR/issue-38821.rs:9:18
   |
LL | impl<T: NotNull> IntoNullable for T {
   |         -------  ^^^^^^^^^^^^     ^
   |         |
   |         unsatisfied trait bound introduced here
   = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting the associated type
   |
LL |     Expr: Expression<SqlType=<Col::SqlType as IntoNullable>::Nullable>, <Col as Expression>::SqlType: NotNull,
   |                                                                       +++++++++++++++++++++++++++++++++++++++

error: aborting due to previous error

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