private File prepare(Id id) throws IOException {
   if (id == null) {
     throw new IllegalArgumentException("id is null");
   }
   logger.info("Preparing " + id);
   return fileOrchestrator.prepare(id, repo.src(id), conf(id));
 }
 private void validate(final Id id) {
   if (id == null) {
     throw new IllegalArgumentException("id is null");
   }
   try {
     dockerfileValidator.validate(repo.src(id));
   } catch (IOException e) {
     throw new OrchestrationException(e);
   }
 }