How to get user id in an order mailer - Spree

This is the line that gives the error. I know this would normally grab the id (I have used the same line in controllers) but I am not sure why it wouldn't work within the order mailer.

pdfs = Pdf.where(user_id: spree_current_user.id, created_at: Date.today-1.hour)

If there are any other files that you might need to look at then please let me know. Would very much appreciate any help !

Thanks in advance.