regression: empty/falsy ClientRequest method '' throws instead of defaulting to GET (over-validation from #4907)

[proggeramlug]

Summary

Regression surfaced by re-measuring node:http parity on current main. test-http-client-defaults was fixed by #4904 (Agent/ClientRequest constructable), but the header-validation added in #4907 now over-fires on an empty/falsy method:

const req = new ClientRequest({ method: '', createConnection: () => {} });
assert.strictEqual(req.method, 'GET');   // Node defaults falsy method → 'GET'

Perry throws:

TypeError: Method must be a valid HTTP token [""]

Node treats a falsy method ('', undefined) as the default 'GET' — it does not validate-reject it. The validateHeaderName-style HTTP-token check from #4907 must only apply to a non-empty method; empty/falsy must fall through to the 'GET' default.

Repro

test-http-client-defaults.js (Node v22 test/parallel) — currently runtime-fail, was pass at the prior measurement.

Acceptance

new ClientRequest({ method: '' }) and ({ method: undefined }) default req.method to 'GET'; only a non-empty invalid token throws ERR_INVALID_HTTP_TOKEN. test-http-client-defaults back to pass, no re-break of #4907's validation tests.

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Regression from #4907. Found re-measuring #2132's corpus on main (parity 26.2%).