fix: respect explicit null end in optimized slice

__tests__/array-methods-slice.js

@@ -0,0 +1,33 @@
+import {Immer, enableArrayMethods} from "../src/immer"
+import {clearPlugin, PluginArrayMethods} from "../src/internal"
+
+for (const useArrayMethods of [false, true]) {
+	for (const autoFreeze of [false, true]) {
+		describe(`array methods: plugin=${useArrayMethods}, autoFreeze=${autoFreeze}`, () => {
+			const {produce} = new Immer({autoFreeze})
+			beforeEach(() => {
+				if (useArrayMethods) enableArrayMethods()
+				else clearPlugin(PluginArrayMethods)
+			})
+			afterEach(() => clearPlugin(PluginArrayMethods))
+			test("distinguishes null end from omitted or undefined end", () => {
+				const base = {items: [{id: 1}, {id: 2}, {id: 3}]}
+				const result = produce(base, draft => {
+					for (const args of [
+						[0, null],
+						[1, null],
+						[-2, null],
+						[null, null],
+						[0],
+						[0, undefined]
+					]) {
+						expect(draft.items.slice(...args).map(item => item.id)).toEqual(
+							base.items.slice(...args).map(item => item.id)
+						)
+					}
+				})
+				expect(result).toBe(base)
+			})
+		})
+	}
+}

src/plugins/arrayMethods.ts

@@ -478,7 +478,7 @@ export function enableArrayMethods() {
 
 		if (method === "slice") {
 			const rawStart = args[0] ?? 0
-			const rawEnd = args[1] ?? source.length
+			const rawEnd = args[1] === undefined ? source.length : args[1]
 
 			// Normalize negative indices
 			const start = normalizeSliceIndex(rawStart, source.length)