Some plugins seem to have added '/' in the end.

Inferred from the following stack trace:

whitesource
java.io.FileNotFoundException: /var/lib/jenkins/.wiki.jenkins-ci.org-cache/Whitesource Plugin/.page.tmp (No such file or directory)
	at java.io.FileOutputStream.open(Native Method)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:179)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:131)
	at org.jvnet.hudson.update_center.ConfluencePluginList.writeToCache(ConfluencePluginList.java:184)
	at org.jvnet.hudson.update_center.ConfluencePluginList.loadPage(ConfluencePluginList.java:172)
	at org.jvnet.hudson.update_center.ConfluencePluginList.getPage(ConfluencePluginList.java:136)
	at org.jvnet.hudson.update_center.Plugin.findPage(Plugin.java:181)
	at org.jvnet.hudson.update_center.Plugin.<init>(Plugin.java:124)
	at org.jvnet.hudson.update_center.Main.buildPlugins(Main.java:225)
	at org.jvnet.hudson.update_center.Main.buildUpdateCenterJson(Main.java:176)
	at org.jvnet.hudson.update_center.Main.run(Main.java:144)
	at org.jvnet.hudson.update_center.Main.run(Main.java:121)
	at org.jvnet.hudson.update_center.Main.main(Main.java:108)