autowired(required=false)?报错

类Performer：

public interface Performer { void perform();
}

类Instrumentallist：

public class Instrumentalist implements Performer{ private String song; private 

Instrument instrument; public Instrumentalist() {
    } public void setSong(String song){ this.song = song;
    } public String getSong(){ return song;
    } @Autowired(required = false) public void setInstrument(Instrument instrument)

{ this.instrument = instrument;
    } public String screamSong(){ return song;
    } @Override  public void perform() {
        System.out.println("Playing "+ song+":"); instrument.play();
    }

}

<?xml version="1.0" encoding="UTF-8"?> 

<beans xmlns="http://www.springframework.org/schema/beans"  

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

 xmlns:context="http://www.springframework.org/schema/context" 

 xsi:schemaLocation="http://www.springframework.org/schema/beans  

http://www.springframework.org/schema/beans/spring-beans.xsd  

http://www.springframework.org/schema/context  

http://www.springframework.org/schema/context/spring-context.xsd">

<context:annotation-config></context:annotation-config>

<bean id="kenny2" class="com.springinaction.autowire.Instrumentalist">

<property name="song" value="Jingle Bells"></property> </bean> </beans>

public class autowireMain { public static void main(String[] args){

ApplicationContext context = new ClassPathXmlApplicationContext(

"com/springinaction/autowire/spring-annotationIdol.xml");
        Instrumentalist instrument = (Instrumentalist) context.getBean("kenny2");
        instrument.perform();
    }
}

输出：

十月 19, 2016 4:12:32 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@f9e681c: startup date [Wed Oct 19 16:12:32 CST 2016]; root of context hierarchy
十月 19, 2016 4:12:32 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [com/springinaction/autowire/spring-annotationIdol.xml]
Playing Jingle Bells:
Exception in thread "main" java.lang.NullPointerException
	at com.springinaction.autowire.Instrumentalist.perform(Instrumentalist.java:32)
	at com.springinaction.autowire.autowireMain.main(autowireMain.java:12)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Process finished with exit code 1

问题：

为什么使用了@Autowired（required=false）还是有报错，不是应该没有报错吗？

还是我对这个用法理解有误？