ConditionalKeys: fix compatibility with TypeScript 5.4

source/conditional-keys.d.ts

@@ -30,11 +30,10 @@ type StringKeysAndUndefined = ConditionalKeys<Example, string | undefined>;
 
 @category Object
 */
-export type ConditionalKeys<Base, Condition> = NonNullable<
-// Wrap in `NonNullable` to strip away the `undefined` type from the produced union.
+export type ConditionalKeys<Base, Condition> =
 {
  // Map through all the keys of the given base type.
- [Key in keyof Base]:
+ [Key in keyof Base]-?:
  // Pick only keys with types extending the given `Condition` type.
  Base[Key] extends Condition
  // Retain this key since the condition passes.
@@ -43,5 +42,4 @@ export type ConditionalKeys<Base, Condition> = NonNullable<
  : never;
 
  // Convert the produced object into a union type of the keys which passed the conditional test.
-}[keyof Base]
->;
+}[keyof Base];

tsconfig.json

@@ -27,8 +27,7 @@
  "useDefineForClassFields": true,
  },
  "exclude": [
- // Ignore `ConditionalKeys` and `WriteableDeep` error temporarily, remove when #831 and #833 are fixed.
- "test-d/conditional-keys.ts",
+ // Ignore `WriteableDeep` error temporarily, remove when #833 are fixed.
  "test-d/writable-deep.ts",
  ]
 }