Cannot install plugin Via Administration -> plugin repository -> Upload -> Remote Url

When I try to install plugin using plugin repository by using Upload method(You can reach the page by following this path: Administration console -> Plugin Repository -> Upload ), Confluence displays an error pop up windows as attached in this issue (reproduce.jpg). The plugin is not installed.

Below is the steps to reproduce the problem:

1. Go to Administration console -> Plugin Repository. It will load the plugins list.
2. Click tab Upload, you will see Remote URL field. You can try to use the following link from sql plugin:

   http://confluence.developer.atlassian.com/plugins/servlet/proxy-counter/org.swift.confluence.sql/9/http://svn.atlassian.com/svn/public/contrib/confluence/sql-plugin/jars/sql-plugin-3.5.0.jar
   

3. Click button Install and wait, you will see the pop up error as the attached file

The following is the stractrace that I got in the log in regard of this bug:

java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)
at com.atlassian.plugin.manager.DefaultPluginManager.getPlugin(DefaultPluginManager.java:703)
....
JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
at $Proxy10.getPlugin(Unknown Source)
....
at com.atlassian.plugin.osgi.hostcomponents.impl.DefaultComponentRegistrar$ContextClassLoaderSettingInvocationHandler.invoke(DefaultComponentRegistrar.java:129)
at $Proxy91.getPlugin(Unknown Source)
at com.atlassian.plugin.repository.logic.AbstractRepositoryPluginManager.installPlugin(AbstractRepositoryPluginManager.java:54)
at com.atlassian.plugin.repository.plugin.RepositoryUploadAction.installPlugin(RepositoryUploadAction.java:65)
at com.atlassian.plugin.repository.plugin.RepositoryUploadAction.handleUploadedFile(RepositoryUploadAction.java:49)