[xiehuanyi]

expect(() => { throw null; }).to.throw(TypeError) currently passes because the constructor/message checks require a truthy thrown value. The same false positive affects undefined, false, 0, NaN, and the empty string. Negated message assertions also miss an empty thrown string.

Use the existing errorWasThrown flag to decide whether to check constraints. Guard nullish values before calling the error helpers, so mismatches produce an AssertionError instead of a property-access TypeError. Add regressions for constructors, error instances, strings/regular expressions, and negated empty-string matches.

Validation:

• New regressions on the unchanged source: 3 failing tests.
• npm run build and npm run lint: pass.
• npm run test-node: 515 passing, coverage check passes.
• Browser suite: 514 passing in installed Google Chrome, using the project's normal configuration plus a local Playwright executable-path override. The default command could not start because its downloaded Chromium revision is absent.
• git diff --check: pass.

AI assistance: OpenAI gpt-6.1-sol with xhigh reasoning was used to investigate, implement, and validate this change.

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