Adding an extra forward slash '/' in the download attachment URL results in a stack trace.

java.lang.NullPointerException
	at com.atlassian.confluence.servlet.download.AttachmentDownload.getStreamForDownload(AttachmentDownload.java:118)
	at com.atlassian.confluence.servlet.download.ServeAfterTransactionDownload$StreamResultCallback.doInTransaction(ServeAfterTransactionDownload.java:111)
	at com.atlassian.confluence.servlet.download.ServeAfterTransactionDownload$StreamResultCallback.doInTransaction(ServeAfterTransactionDownload.java:94)
	at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140)
	at com.atlassian.confluence.servlet.download.ServeAfterTransactionDownload.getStreamInTransaction(ServeAfterTransactionDownload.java:39)
	at com.atlassian.confluence.servlet.download.ServeAfterTransactionDownload.serveFile(ServeAfterTransactionDownload.java:45)
	at com.atlassian.plugin.servlet.AbstractFileServerServlet.doGet(AbstractFileServerServlet.java:28)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	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 com.atlassian.confluence.web.filter.DebugFilter.doFilter(DebugFilter.java:46)
	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:32)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:39)
	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.lambda$doFilter$0(DelegatingPluginFilter.java:57)
	at com.atlassian.confluence.image.effects.ImageFilterFilter.doFilter(ImageFilterFilter.java:43)
	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.doFilter(DelegatingPluginFilter.java:62)
	at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:37)
	at com.atlassian.plugin.servlet.filter.DelegatingPluginFilter.lambda$doFilter$0(DelegatingPluginFilter.java:57)
	at com.atlassian.confluence.plugins.baseurl.IncludeResourcesFilter.doFilter(IncludeResourcesFilter.java:52)
	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:32)