mandatory candidate (even if undefined)

Author: amannn

Diff for: packages/use-intl/src/core/hasLocale.test.tsx

@@ -28,6 +28,7 @@ it('can be called with a non-matching narrow candidate', () => {
 it('can be called with any candidate', () => {
   const locales = ['en-US', 'en-GB'] as const;
   expect(hasLocale(locales, 'unknown')).toBe(false);
+  expect(hasLocale(locales, undefined)).toBe(false);
 
   // Relevant since `ParamValue` in Next.js includes `string[]`
   expect(hasLocale(locales, ['de'])).toBe(false);

Diff for: packages/use-intl/src/core/hasLocale.tsx

@@ -7,7 +7,7 @@ import type {Locale} from './AppConfig.tsx';
  */
 export default function hasLocale<LocaleType extends Locale>(
   locales: ReadonlyArray<LocaleType>,
-  candidate?: unknown
+  candidate: unknown
 ): candidate is LocaleType {
   return locales.includes(candidate as LocaleType);
 }