Merge pull request #13117 from keymanapp/fix/common/13116-handle-unde…

…fined-input-in-langtags-lookup

fix(common): handle undefined input in `@keymanapp/langtags` lookups

common/web/langtags/src/main.ts

@@ -114,7 +114,7 @@ function preinit(): void {
  * @returns LangTag or undefined if not found
  */
 function getLangtagByTag(tag: string): LangTag {
-  return langtagsByTag.get(tag.toLowerCase());
+  return langtagsByTag.get(tag?.toLowerCase());
 }
 
 preinit();