changed the id from String to Long

application/module-language-school/src/main/java/org/fuseri/modulelanguageschool/user/UserService.java

@@ -19,7 +19,7 @@ public class UserService extends DomainService<User> {
     }
 
     @Transactional(readOnly = true)
-    public User find(String id) {
+    public User find(Long id) {
         return repository.findById(id)
                 .orElseThrow(() -> new EntityNotFoundException("User '" + id + "' not found."));
     }