public static String getParentPlugin( Path pluginDir )
    {
        final String name = getElementValue( pluginDir, "/plugin/parentPlugin" );
        if ( name != null && !name.isEmpty() )
        {
            return name.toLowerCase();
        }
        return null;
    }
Returns the name of the directory of the parent for this plugin. The value is retrieved from the plugin.xml file
of the plugin (which is casted down to lower-case). If the value could not be found, {@code null} will be returned.

@param pluginDir the path of the plugin directory.
@return the parent plugin's directory name
xmppserver/src/main/java/org/jivesoftware/openfire/container/PluginMetadataHelper.java