refactor: return early when children == null

[chenfan0]

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Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	85.9 kB (+17 B)	32.6 kB (+4 B)	29.5 kB (+19 B)
vue.global.prod.js	132 kB (+17 B)	49.3 kB (+5 B)	44.3 kB (-1 B)

Usages

Name	Size	Gzip	Brotli
createApp	47.9 kB (+17 B)	18.8 kB (+2 B)	17.2 kB (+5 B)
createSSRApp	50.7 kB (+17 B)	19.9 kB (+1 B)	18.2 kB (+7 B)
defineCustomElement	50.3 kB (+17 B)	19.6 kB (+2 B)	18 kB (+65 B)
overall	61.3 kB (+17 B)	23.7 kB (+5 B)	21.6 kB (+16 B)

[sxzz]

Thanks for your contribution! We presently do not entertain stylistic refinements, unless they demonstrably contribute significantly to performance or bundle size reduction. Could you provide evidence to substantiate this?

[yyx990803]

children being nullish is a relatively rare codepath so I don't think this will result in meaningful performance difference. The original code compresses better.