Popover/Tooltip placement logs tether error

Created by: chapterjason

I tried the auto placement like described in the documentation

When "auto" is specified, it will dynamically reorient the popover. For example, if placement is "auto left", the popover will display to the left when possible, otherwise it will display right.

After nothing happens I saw an error in the console.

Error: Tether Error: You must provide an attachment

On a bit debugging I found out that attachment is undefined in the tooltip.js what extends the popover.js cause the AttachmentMap does not provide any auto left

https://github.com/twbs/bootstrap/blob/v4-dev/js/src/tooltip.js#L282