fix: throw proper immer error when applyPatches path traverses null

[JSap0914]

Bug

applyPatches throws a native TypeError instead of immer's own error when a patch path navigates through a null intermediate value.

Root cause: isObjectish is implemented as typeof target === "object". Because typeof null === "object" in JavaScript, isObjectish(null) returns true. The guard inside applyPatches_ that is supposed to catch non-navigable intermediates therefore lets null slip through. The next iteration (or the post-loop getArchtype call) then does null[DRAFT_STATE] and crashes with:

TypeError: Cannot read properties of null (reading 'Symbol(immer-state)')

instead of immer error 18:

Cannot apply patch, path doesn't resolve: a/b

Fix

Add an explicit base === null check alongside !isObjectish(base) in the path-traversal loop of applyPatches_ (src/plugins/patches.ts):

-if (!isObjectish(base)) die(errorOffset + 2, path.join("/"))
+if (base === null || !isObjectish(base)) die(errorOffset + 2, path.join("/"))

Verification

yarn test:src
# Test Files  22 passed (22)
# Tests  3652 passed | 8 skipped (3660)

New test added in __tests__/patch.js:

• applyPatches({a: null}, [{op: 'add', path: ['a', 'b'], value: 1}]) now throws with message "Cannot apply patch, path doesn't resolve: a/b"

This PR was prepared with AI assistance.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.