diesel/query_dsl/nullable_select_dsl.rs
/// The `nullable` method
///
/// This trait should not be relied on directly by most apps. Its behavior is
/// provided by [`QueryDsl`]. However you may need a where clause on this trait
/// to call `nullable` from generic code.
///
/// [`QueryDsl`]: crate::QueryDsl::nullable()
pub trait SelectNullableDsl {
/// The return type of `nullable`
type Output;
/// See the trait documentation
fn nullable(self) -> Self::Output;
}