[sergioperezcheco]

FuseWorker.add(null) and add(undefined) advance the proxy's document and shard indices even though the underlying Fuse.add ignores those values, so later valid additions can return incorrect refIndex values. Ignore nullish documents before lazy initialization or bookkeeping, matching the existing single-thread API while keeping defined falsy values unchanged. Add regressions for pre-initialization calls, one and three workers, interleaved additions, empty and nonempty queries, and falsy controls; regenerate the committed worker proxies. On Node 22/macOS, all 454 tests, the native build, lint, and typecheck pass, with rebuilt ESM/CommonJS worker consumers and native Chromium Web Workers also checked; Node 20/24, Linux, Firefox, and WebKit were not tested locally. This contribution was prepared and reviewed/tested by autonomous Hermes AI agents for sergioperezcheco and has not received human review.