Attach attached files from issue to transition Screen

[Dominykas Šmičius]

Hi, I have made a transition to send mail with groovy, but I want to choose which files to attach to mail. How to attach attached files in a issue to the send screen and allow to select which files to send.

Simple code not working 

def attachments = attachmentManager.getAttachments(issue)
attachments.each { attachment ->
getFieldById("attachment").setFormValue(attachment)
}

Thanks