[just-diff] op type error.I add a new property with an empty string,but the op is replace

[skymoonya]

it should be add

code

import { diff } from 'just-diff';
import { diffApply } from 'just-diff-apply';
const json1 = { a: '123' }
const json2 = { a: '', b: '' }
console.log(diff(json1, json2))
diffApply(json1, diff(json1, json2))

just-diff version: 6.0.0

[angus-c]

Fixed in #545