Exception in logs when closing image upload dialog box early

1. In the content editor, choose images from the drop down and choose a folder to upload a new image too.
2. Select some images or perhaps one larger one (so that uploading lasts at least a couple of seconds or more).
3. Close the dialog box before uploading has completed.

This error is reported in hippo-cms.log:

02.05.2018 13:06:49 +0000 [catalina-exec-4] ERROR [org.apache.wicket.DefaultExceptionMapper.mapUnexpectedExceptions():170] Unexpected error occurred
org.apache.wicket.core.request.handler.ComponentNotFoundException: Component 'dialog:content:form:uploadPanel' has been removed from page.
{{ at org.apache.wicket.core.request.handler.ListenerInterfaceRequestHandler.respond(ListenerInterfaceRequestHandler.java:178) ~[wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:890) ~[wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64) ~[wicket-request-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:261) [wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:218) [wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:289) [wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:259) [wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:201) [wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:282) [wicket-core-6.26.0.jar:6.26.0]}}
{{ at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [catalina.jar:8.0.48]}}
{{ at org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:54) [hippo-cms-engine-5.1.1.jar:5.1.1]}}
{{ at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) [catalina.jar:8.0.48]}}
{{ at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502) [catalina.jar:8.0.48]}}
{{ at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132) [tomcat-coyote.jar:8.0.48]}}
{{ at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684) [tomcat-coyote.jar:8.0.48]}}
{{ at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1539) [tomcat-coyote.jar:8.0.48]}}
{{ at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1495) [tomcat-coyote.jar:8.0.48]}}
{{ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_161]}}
{{ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_161]}}
{{ at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:8.0.48]}}
{{ at java.lang.Thread.run(Thread.java:748) [?:1.8.0_161]}}