/// Trait for types that can be `None`.
////// This trait is used to indicate that a type can reserve a specific value to
/// represent `None`.
pubtraitNullable: PartialEq + Sized {/// Value that represents `None` for the type.
constNONE:Self;/// Indicates whether the value is `None` or not.
fnis_none(&self)->bool{self==&Self::NONE}/// Indicates whether the value is a `Some` value of type `Self` or not.
fnis_some(&self)->bool{!self.is_none()}}