[pull] main from facebook:main

packages/lexical-utils/src/__tests__/unit/LexicalUtilsKlassEqual.test.ts

@@ -28,5 +28,14 @@ describe('LexicalUtilsKlassEqual tests', () => {
       expect(eventInstance instanceof MyEventShadow).toBeFalsy();
       expect(objectKlassEquals(eventInstance, MyEventShadow)).toBeTruthy();
     });
+    it('objectKlassEquals with a nullish or prototype-less value', async () => {
+      // The parameter is typed `unknown`, and the existing `!== null` guard
+      // shows nullish input is expected to be answered, not thrown on.
+      expect(objectKlassEquals(null, MyEvent)).toBe(false);
+      expect(objectKlassEquals(undefined, MyEvent)).toBe(false);
+      // Object.getPrototypeOf() returns null for these, so reading
+      // .constructor off it throws.
+      expect(objectKlassEquals(Object.create(null), MyEvent)).toBe(false);
+    });
   });
 });

packages/lexical-utils/src/index.ts

@@ -848,9 +848,14 @@ export function objectKlassEquals<T>(
   object: unknown,
   objectClass: ObjectKlass<T>,
 ): object is T {
-  return object !== null
-    ? Object.getPrototypeOf(object).constructor.name === objectClass.name
-    : false;
+  if (object == null) {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(object);
+  if (prototype == null || prototype.constructor == null) {
+    return false;
+  }
+  return prototype.constructor.name === objectClass.name;
 }
 
 // Clipboard may contain files that we aren't allowed to read. While the event is arguably useless,