How to solve java.lang.NullPointerException error in my ManagedBean?

When I run my program, it gives me a NullPointerException error The problem happens when I run index.xhtml

java.lang.NullPointerException
at com.mhfd.tuto.bean.HelloController.ShowHello(HelloController.java:23)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:476)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:161)
at org.apache.el.parser.AstValue.getValue(AstValue.java:173)
at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:185)
at com.sun.faces.facelets.el.ELText$ELTextVariable.writeText(Unknown Source)
at com.sun.faces.facelets.el.ELText$ELTextComposite.writeText(Unknown Source)
at com.sun.faces.facelets.compiler.TextInstruction.write(Unknown Source)
at com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(Unknown Source)
at com.sun.faces.facelets.compiler.UILeaf.encodeAll(Unknown Source)
at javax.faces.component.UIComponent.encodeAll(Unknown Source)
at javax.faces.component.UIComponent.encodeAll(Unknown Source)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(Unknown Source)
at com.sun.faces.application.view.MultiViewHandler.renderView(Unknown Source)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(Unknown Source)
at com.sun.faces.lifecycle.Phase.doPhase(Unknown Source)
at com.sun.faces.lifecycle.LifecycleImpl.render(Unknown Source)
at javax.faces.webapp.FacesServlet.service(Unknown Source)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

> ----------------------- ManagedBean

    @ManagedBean
public class HelloController {

    @Autowired
    private HelloSpringService helloSpringService;

    public String ShowHello() {
        return helloSpringService.SayHello();
    }

    public void setHelloSpringService(HelloSpringService helloSpringService) {
        this.helloSpringService = helloSpringService;
    }
}

> ------------------------------------- service

@Service
public class HelloSpringService {

    public String SayHello() {
        return "hello spring";
    }
}

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