fix: don't crash serializing an explicit null/undefined param value

[SurajPatelPro]

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Fixes #1052 🦕

What & why

serializer() called each key's format function unconditionally whenever the key existed on the params object, so { location: undefined } — a common way to conditionally omit an optional field — reached latLngToString and threw Cannot use 'in' operator to search for 'lat' in undefined, instead of being treated as "not supplied". @usefulthink correctly identified the root cause in the issue thread.

What changed

src/serialize.ts — in serializer(), a key whose value is null/undefined is now deleted from serializedParams before the format step, rather than being passed through to the format function.

I initially tried leaving the nullish value in place and letting query-string's own stringify drop it, but that turned out to be inconsistent: query-string omits undefined from the output query string by default, but keeps null as a bare, value-less key (e.g. location with no =). Deleting the key outright avoids that mismatch and treats both the same way — as if the key were never supplied.

How it was verified

• Added a test in src/serialize.test.ts covering both location: undefined and location: null against a formatted key, asserting the key is dropped entirely from the resulting query string.
• npx jest src/ — 21/21 test suites, 70/70 tests passing.
• npx tsc --noEmit — clean.
• npx eslint src/serialize.ts src/serialize.test.ts — clean.
• The repo's e2e/* suite requires a live Google Maps API key and network access, unavailable in my environment — confirmed those failures are unrelated to this change (same failure mode before and after, purely network/API-key dependent).

Note

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