今天服务器在运行过程中抛出了如下错误，导致无法访问

[ERROR]-[2019-04-25 15:22:00]-[org.b3log.symphony.service.ArticleQueryService:1569]: Organizes article [1555745058690] failed
java.lang.NullPointerException
[ERROR]-[2019-04-25 15:22:00]-[org.b3log.symphony.service.ArticleQueryService:1569]: Organizes article [1555744835700] failed
java.lang.NullPointerException
[ERROR]-[2019-04-25 15:22:00]-[org.b3log.latke.servlet.renderer.AbstractFreeMarkerRenderer:131]: Renders template [search-articles.ftl] failed [Request [
    method=GET,
    URL=http://qiankunpingtai.cn:443/symphony/search,
    contentType=null,
    characterEncoding=UTF-8,
    local=[
        addr=127.0.0.1,
        port=8081,
        name=localhost],
    remote=[
        addr=61.130.*.*,
        port=45628,
        host=127.0.0.1],
    headers=[
        host=qiankunpingtai.cn:443
        remote-host=61.130.*.*
        x-real-ip=61.130.*.*
        x-forwarded-for=61.130.*.*
        connection=close
        accept=*/*
        user-agent=Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727)
        accept-encoding=gzip, deflate
    ]
]]
FreeMarker template error:
The following has evaluated to null or missing:
==> article.articleTagObjs  [in template "classic/common/list-item.ftl" at line 22, column 16]


Tip: It's the step after the last dot that caused this error, not those before it.

Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??



FTL stack trace ("~" means nesting-related):
	- Failed at: #list article.articleTagObjs as artic...  [in template "classic/common/list-item.ftl" at line 22, column 9]
	- Reached through: #include "common/list-item.ftl"  [in template "classic/macro-list.ftl" in macro "list" at line 28, column 9]
	- Reached through: @list listData=articles  [in template "classic/search-articles.ftl" at line 42, column 25]


Java stack trace (for programmers):

freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
	at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
	at freemarker.core.Expression.assertNonNull(Expression.java:233)
	at freemarker.core.IteratorBlock.acceptWithResult(IteratorBlock.java:103)
	at freemarker.core.IteratorBlock.accept(IteratorBlock.java:93)
	at freemarker.core.Environment.visit(Environment.java:330)
	at freemarker.core.Environment.visit(Environment.java:336)
	at freemarker.core.Environment.include(Environment.java:2582)
	at freemarker.core.Include.accept(Include.java:171)
	at freemarker.core.Environment.visit(Environment.java:366)
	at freemarker.core.IteratorBlock$IterationContext.executedNestedContentForCollOrSeqListing(IteratorBlock.java:317)
	at freemarker.core.IteratorBlock$IterationContext.executeNestedContent(IteratorBlock.java:271)
	at freemarker.core.IteratorBlock$IterationContext.accept(IteratorBlock.java:242)
	at freemarker.core.Environment.visitIteratorBlock(Environment.java:642)
	at freemarker.core.IteratorBlock.acceptWithResult(IteratorBlock.java:107)
	at freemarker.core.IteratorBlock.accept(IteratorBlock.java:93)
	at freemarker.core.Environment.visit(Environment.java:366)
	at freemarker.core.Environment.invoke(Environment.java:775)
	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:83)
	at freemarker.core.Environment.visit(Environment.java:330)
	at freemarker.core.Environment.visit(Environment.java:336)
	at freemarker.core.Environment.visit(Environment.java:336)
	at freemarker.core.Environment.process(Environment.java:309)
	at freemarker.template.Template.process(Template.java:384)
	at org.b3log.latke.servlet.renderer.AbstractFreeMarkerRenderer.genHTML(AbstractFreeMarkerRenderer.java:154)
	at org.b3log.symphony.processor.SkinRenderer.genHTML(SkinRenderer.java:137)
	at org.b3log.latke.servlet.renderer.AbstractFreeMarkerRenderer.render(AbstractFreeMarkerRenderer.java:125)
	at org.b3log.latke.servlet.DispatcherServlet.result(DispatcherServlet.java:118)
	at org.b3log.latke.servlet.DispatcherServlet.handle(DispatcherServlet.java:97)
	at org.b3log.latke.servlet.DispatcherServlet.service(DispatcherServlet.java:69)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:668)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)
[WARN ]-[2019-04-25 15:22:06]-[org.b3log.latke.servlet.handler.BeforeHandleHandler:60]: Occurred an exception before request processing: 401, /symphony/post