HTML export does not work if XWiki WAR is not unpacked

2018-04-03 12:11:38,048 [http://127.0.0.1:8080/xwiki/bin/export/Sandbox/WebHome?format=html] WARN  c.x.x.w.XWikiAction            - Uncaught exception: Error number 11015 in 11: Exception while exporting 
com.xpn.xwiki.XWikiException: Error number 11015 in 11: Exception while exporting
	at com.xpn.xwiki.web.ExportAction.render(ExportAction.java:90)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:446)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:209)
	at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
	at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
	at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
	at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:860)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1650)
	at com.xpn.xwiki.web.ActionFilter.doFilter(ActionFilter.java:112)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
	at org.xwiki.wysiwyg.filter.ConversionFilter.doFilter(ConversionFilter.java:127)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
	at org.eclipse.jetty.websocket.server.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:206)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
	at org.xwiki.container.servlet.filters.internal.SetHTTPHeaderFilter.doFilter(SetHTTPHeaderFilter.java:63)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
	at org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
	at org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:111)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1637)
	at org.xwiki.resource.servlet.RoutingFilter.doFilter(RoutingFilter.java:134)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1629)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:190)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1253)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1564)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1155)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:219)
	at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
	at org.eclipse.jetty.server.Server.handle(Server.java:530)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:347)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:256)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:102)
	at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:247)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.produce(EatWhatYouKill.java:140)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:131)
	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:382)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:708)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:626)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException: null
	at java.io.File.<init>(File.java:277)
	at com.xpn.xwiki.export.html.HtmlPackager.addSkinToZip(HtmlPackager.java:488)
	at com.xpn.xwiki.export.html.HtmlPackager.export(HtmlPackager.java:394)
	at com.xpn.xwiki.web.ExportAction.exportHTML(ExportAction.java:134)
	at com.xpn.xwiki.web.ExportAction.render(ExportAction.java:85)
	... 54 common frames omitted