Plugins cannot be installed via Plugin Installer

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.1.10 EE GA1, 6.2.0 CE M2
• Fix Version/s: 6.1.1 CE GA2, 6.1.10 EE GA1, 6.1.20 EE GA2, 6.2.0 CE M2
• Component/s: Legacy Components > Administration UI
• Labels:
  • QA-NA
  • QA-R
  • fixpack-candidate
• Branch Version/s:
  6.1.x
• Backported to Branch:
  Committed
• Fix Priority: 5
• Added to Fix Pack:
  Added
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/4321

Steps to reproduce:

1. Log in as administrator.
2. Go to Control Panel -> Plugins Installation.
3. Click Install More Portlets.
4. Click Upload File.
5. Browse to a plugin .war file.
6. Click Install.

The installation fails because the Struts action is either missing or not configured. Here's the relevant part of the stack trace:

18:59:37,819 ERROR [RequestProcessor:296] No action instance for path /plugin_installer/view could be created
java.lang.NullPointerException
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1616)
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1546)
        at org.apache.struts.util.RequestUtils.applicationClass(RequestUtils.java:117)
        at org.apache.struts.util.RequestUtils.applicationInstance(RequestUtils.java:143)
        at org.apache.struts.action.RequestProcessor.processActionCreate(RequestProcessor.java:292)
        at com.liferay.portal.struts.PortletRequestProcessor.processActionCreate(PortletRequestProcessor.java:405)
        at com.liferay.portal.struts.PortletRequestProcessor.process(PortletRequestProcessor.java:149)
        at com.liferay.portlet.StrutsPortlet.processAction(StrutsPortlet.java:190)
        at com.liferay.portlet.FilterChainImpl.doFilter(FilterChainImpl.java:70)
        at com.liferay.portal.kernel.portlet.PortletFilterUtil.doFilter(PortletFilterUtil.java:48)
        at com.liferay.portlet.InvokerPortletImpl.invoke(InvokerPortletImpl.java:651)
        at com.liferay.portlet.InvokerPortletImpl.invokeAction(InvokerPortletImpl.java:686)
        at com.liferay.portlet.InvokerPortletImpl.processAction(InvokerPortletImpl.java:361)
        at com.liferay.portal.action.LayoutAction.processPortletRequest(LayoutAction.java:856)
        at com.liferay.portal.action.LayoutAction.processLayout(LayoutAction.java:635)
        at com.liferay.portal.action.LayoutAction.execute(LayoutAction.java:246)
        at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
        at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
        at com.liferay.portal.struts.PortalRequestProcessor.process(PortalRequestProcessor.java:174)
        at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
        at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)