fix(lexical): guard klass.prototype null check in getStaticNodeConfig

[potatowagon]

Summary

getStaticNodeConfig() uses the in operator on klass.prototype without checking that it is non-null. When the extends-chain traversal reaches a class whose prototype is undefined (e.g. a functional component or exotic constructor), this throws:

TypeError: Cannot use 'in' operator to search for '$config' in undefined

Fix

Add a null guard so the lookup safely falls through to undefined instead of throwing:

-    PROTOTYPE_CONFIG_METHOD in klass.prototype
+    klass.prototype != null && PROTOTYPE_CONFIG_METHOD in klass.prototype

Context

This is a regression introduced in #8716 (Named-slot typing). The crash surfaces when createEditor() traverses the $config.extends chain and walks past a proper class boundary where klass.prototype is undefined.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview, Comment	Jun 20, 2026 8:49am
lexical-playground	Ready	Preview, Comment	Jun 20, 2026 8:49am

[etrepum]

This seems fine but I’d like to see an example of an object that is a valid node and crashes without this patch

[etrepum]

AFAICT this only serves to improve the error message, I can't think of a scenario where this fix changes any behavior.

[potatowagon]

This seems fine but I’d like to see an example of an object that is a valid node and crashes without this patch

Error:

TypeError: Cannot use 'in' operator to search for '$config' in undefined
  at getStaticNodeConfig (Lexical.dev.js:16476:46)
  at getTransformSetFromKlass (Lexical.dev.js:13616:1)
  at createEditor (Lexical.dev.js:13734:35)
  at xdsInternalHeadlessEditorWithXDSNodes

Possible Root cause: #8716 (Named-slot typing). The getTransformSetFromKlass function traverses the $config.extends chain but doesn't guard against currentKlass.prototype === undefined (reached when the chain walks past a proper class boundary, e.g. to Function.prototype). All 98 failures use xdsInternalHeadlessEditorWithXDSNodes → createEditor.

Fix: OSS guard in getStaticNodeConfig:

- const nodeConfigRecord = PROTOTYPE_CONFIG_METHOD in klass.prototype ? ...
+ const nodeConfigRecord = klass.prototype != null && PROTOTYPE_CONFIG_METHOD in klass.prototype ? ...