NoClassDefFoundError in plugin

Hi.

It works correctly in debug environment.
However, "NoClassDefFoundError" in the production environment will occur.

Stack trace is here.

com/intellij/openapi/actionSystem/DataKeys: com/intellij/openapi/actionSystem/DataKeys
java.lang.NoClassDefFoundError: com/intellij/openapi/actionSystem/DataKeys
 at com.vexus2.intellij.openingithub.OpenInGitHub.actionPerformed(OpenInGitHub.java:36)
 at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher$3.performAction(IdeKeyEventDispatcher.java:564)
 at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.processAction(IdeKeyEventDispatcher.java:611)
 at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.d(IdeKeyEventDispatcher.java:463)
 at com.intellij.openapi.keymap.impl.IdeKeyEventDispatcher.dispatchKeyEvent(IdeKeyEventDispatcher.java:206)
 at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.java:493)
 at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:335)
 at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
 at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
 at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
 at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
 at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
 at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Caused by: java.lang.ClassNotFoundException: com.intellij.openapi.actionSystem.DataKeys PluginClassLoader[com.vexus2.intellij.openingithub, 1.0.5]
 at com.intellij.ide.plugins.cl.PluginClassLoader.loadClass(PluginClassLoader.java:82)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
 ... 13 more