项目上午还能正常运行，下午就一直报这个错：

前端给后台发请求时：后台报错，数据已经拿到了，但是遍历数据的时候出了问题，父节点的id为空，导致所有数据无法显示

java.lang.NullPointerException: null
	at com.shy.gulimall.product.service.impl.CategoryServiceImpl.lambda$listWithTree$0(CategoryServiceImpl.java:43) ~[classes/:na]
	at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174) ~[na:1.8.0_221]
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382) ~[na:1.8.0_221]
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482) ~[na:1.8.0_221]
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) ~[na:1.8.0_221]
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[na:1.8.0_221]
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_221]
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[na:1.8.0_221]
	at com.shy.gulimall.product.service.impl.CategoryServiceImpl.listWithTree(CategoryServiceImpl.java:49) ~[classes/:na]
	at com.shy.gulimall.product.service.impl.CategoryServiceImpl$$FastClassBySpringCGLIB$$cae2de19.invoke(<generated>) ~[classes/:na]
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:684) ~[spring-aop-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at com.shy.gulimall.product.service.impl.CategoryServiceImpl$$EnhancerBySpringCGLIB$$1b47a258.listWithTree(<generated>) ~[classes/:na]
	at com.shy.gulimall.product.controller.CategoryController.list(CategoryController.java:40) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_221]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_221]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_221]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_221]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_221]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_221]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.24.jar:9.0.24]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_221]

原因

之前做增加操作的时候，没有给父节点id赋值，导致遍历时需要判断的id为空，最终导致数据无法三级分类

解决

数据出问题了，重新导入数据，或者把有问题的数据删除即可。