Java - 为什么我不能通过使用别名来枚举KeyStore中的证书？

KeyStore keystore_client = KeyStore.getInstance("pkcs12");

try(InputStream keyInput = new FileInputStream("2.pfx")){
  keystore_client.load(keyInput, null);
}
Enumeration<String> e = keystore_client.aliases();
while(e.hasMoreElements()){
  String alias = e.nextElement();
  if(keystore_client.getCertificate(alias)==null)
    throw new RuntimeException("Cannot get Certificate");
}
KeyStore keystore_client = KeyStore.getInstance