fix: new map keys were not added if value is undefined

__tests__/map-set.js

@@ -235,5 +235,14 @@ function runBaseTest(name, useProxies, autoFreeze, useListener) {
  })
  expect(Array.from(set).sort()).toEqual([1, 2, 3])
  })
+
+ test("#627 - new map key with value=undefined", () => {
+ const map = new Map()
+ const map1 = produce(map, draft => {
+ draft.set("key", undefined)
+ })
+ expect(map1.has("key")).toBe(true)
+ expect(map1.get("key")).toBe(undefined)
+ })
  })
 }

src/plugins/mapset.ts

@@ -80,7 +80,7 @@ export function enableMapSet() {
  p.set = function(key: any, value: any) {
  const state: MapState = this[DRAFT_STATE]
  assertUnrevoked(state)
- if (latest(state).get(key) !== value) {
+ if (!latest(state).has(key) || latest(state).get(key) !== value) {
  prepareMapCopy(state)
  markChanged(state)
  state.assigned_!.set(key, true)