Function neither 

pub const fn neither<L, R>() -> MaybeEither<L, R>

Always returns None, to represent when neither the left nor right value are present.

Using None (or Option::<Either::<L, R>>::None for the long form) is fine.

Example

let maybe_either: MaybeEither<u32, i32> = Either::from_options(None, None);
assert_eq!(maybe_either, neither());