Add nullcheck for window.event

[evankirkiles]

Summary

Adds a null check for window.event. Some browsers seem to be setting this value to null, which breaks the logic of this code snippet, leading to a huge amount of n.type could not be accessed because null is not an object errors.

See:

• May be a bug #24778
• Bug: ReactDOM incorrect check window.event (check undefined, but maybe null) #25664
• Fix: incorrect window.event check #25670

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Name	Status	Preview	Comments	Updated (UTC)
react-compiler-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 23, 2024 2:50pm

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[react-sizebot]

Comparing: f994737...6cce2b3

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.66 kB	6.66 kB	=	1.82 kB	1.82 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	495.89 kB	495.93 kB	=	88.83 kB	88.83 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.67 kB	6.67 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	500.69 kB	500.73 kB	=	89.51 kB	89.52 kB
facebook-www/ReactDOM-prod.classic.js	=	593.05 kB	593.08 kB	=	104.32 kB	104.33 kB
facebook-www/ReactDOM-prod.modern.js	=	569.27 kB	569.31 kB	=	100.72 kB	100.73 kB
test_utils/ReactAllWarnings.js	Deleted	64.35 kB	0.00 kB	Deleted	16.05 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	64.35 kB	0.00 kB	Deleted	16.05 kB	0.00 kB

Generated by 🚫 dangerJS against 6cce2b3

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[classicdocs]

@evankirkiles What is the reason for closing this PR ? I tried to migrate from react 17 to react 18 and in some cases I have issues with this.

[evankirkiles]

@classicdocs Actually, I don't remember—I fixed where we were setting window.event to null in our codebase so didn't end up needing this fix, but I can imagine it might benefit others. Reopening!