import cancel from 'dataparcels/cancel';
import cancel from 'react-dataparcels/cancel';The cancel can be used inside of Parcel.modifyUp to cancel a change. See Parcel.modifyUp for more details.
let parcel = new Parcel({
value: 123
})
parcel = parcel.modifyUp(value => value === null ? cancel : value);
parcel.set(456); // this would work, value becomes 123
parcel.set(null); // this would cause no change