Steps:
1. Copy the jira-toolkit plugin for 3.13 and 4.0 in "installed plugin" folder under JIRA Home.
2. Start the JIRA

Result:
1. It throws an exception "2009-06-12 15:45:59,882 main INFO [atlassian.plugin.manager.DefaultPluginManager] Plugin system started in 0:00:25.360
2009-06-12 15:45:59,882 main ERROR [com.atlassian.jira.ComponentManager] Error occurred while starting PluginManager.
com.atlassian.jira.util.dbc.Assertions$NullArgumentException: name should not be null!"
2. Log is attached

Expected:
1. Better error handling.