A decoder that only accepts undefined values
const undefinedDecoder = JsonDecoder.undefined();
undefinedDecoder.decode(undefined); // Ok<undefined>({value: undefined})
undefinedDecoder.decode(123); // Err({ issues: [{ message: '123 is not undefined', path: [] }] })
undefinedDecoder.decode(null); // Err({ issues: [{ message: 'null is not undefined', path: [] }] })
Decoder for
undefinedvalues.