ArrayIndexOutOfBoundsException: 3 in AttachmentCommandReceiver.java when uploading a wiki attachment

Can not upload attachments to wiki pages via FCKEditor browser's upload button when using Amazon S3 Store or DBStore.

Steps to reproduce:
1. set up portal to use Amazon S3:
create portal-ext.properties:

dl.store.s3.access.key=
dl.store.s3.secret.key=
dl.store.s3.bucket.name=
dl.store.impl=com.liferay.portlet.documentlibrary.store.S3Store

2. add wiki to a page
3. Edit the page
4. click on image button
5. in the file browser browse for a file and upload it
ERROR: The uploaded image does not appears in the file browser's list
And the log says:

ERROR [http-bio-8080-exec-8][ConnectorAction:69] com.liferay.portal.editor.fckeditor.exception.FCKException: java.lang.ArrayIndexOutOfBoundsException: 3
com.liferay.portal.editor.fckeditor.exception.FCKException: java.lang.ArrayIndexOutOfBoundsException: 3
at com.liferay.portal.editor.fckeditor.receiver.impl.AttachmentCommandReceiver.getFoldersAndFiles(AttachmentCommandReceiver.java:102)
at com.liferay.portal.editor.fckeditor.receiver.impl.BaseCommandReceiver.getFoldersAndFiles(BaseCommandReceiver.java:276)
at com.liferay.portal.editor.fckeditor.command.impl.GetFoldersAndFilesCommand.execute(GetFoldersAndFilesCommand.java:38)
at com.liferay.portal.editor.fckeditor.ConnectorAction.execute(ConnectorAction.java:66)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)