fix: do not coerce `undefined` to `null` for JSON serialization #5

Job	Run time
js-test-and-release / check	1m 54s
js-test-and-release / test-chrome-webworker	34s
js-test-and-release / test-electron-renderer	25s
js-test-and-release / test-chrome	40s
js-test-and-release / test-electron-main	34s
js-test-and-release / test-firefox	51s
js-test-and-release / test-firefox-webworker	38s
js-test-and-release / test-webkit (ubuntu-latest, lts/*)	38s
js-test-and-release / test-node (windows-latest, lts/*)	2m 30s
js-test-and-release / test-webkit (macos-latest, lts/*)	2m 36s
js-test-and-release / test-node (ubuntu-latest, lts/*)	32s
js-test-and-release / test-node (macos-latest, lts/*)	3m 2s
js-test-and-release / test-webkit-webworker (ubuntu-latest, lts/*)	43s
js-test-and-release / test-webkit-webworker (macos-latest, lts/*)	1m 48s
js-test-and-release / release-check	0s
js-test-and-release / release	0s
	17m 25s

Provide feedback