There is no PasswordEncoder mapped for the id "null"

因為Spring-Security從4+升級到5+，導致There is no PasswordEncoder mapped for the id “null”錯誤。

解決方案：
1.可在密碼驗證類中添加
@Bean
public static NoOpPasswordEncoder passwordEncoder() {
  return (NoOpPasswordEncoder) NoOpPasswordEncoder.getInstance();
}


2.或者在xml配置文件中添加
<b:bean id="passwordEncoder"    class="org.springframework.security.crypto.password.NoOpPasswordEncoder" factory-method="getInstance"/>