adaptModel.findAncestor triggers an error if no ancestor of that type exists

[moloko]

Subject of the issue/enhancement/features

If you do a findAncestor search on a contentObject to see if it has a contentObject as its ancestor - and it doesn't - an error is thrown.

(Kineo's pageIncompletePrompt extension does this to check to see if learner is being routed to a child page of the current page)

Your environment

Any

Steps to reproduce

Execute the following in the console:

require('core/js/adapt').findById('co-05').findAncestor('contentObjects');

Expected behaviour

no error should occur, the function should simply return undefined to indicate that no results were found

Actual behaviour

The error 'TypeError: returnedAncestor is undefined' is thrown.

[moloko]

Adding in if (!returnedAncestor) return; here would solve the immediate issue, but looking at the code following that the behaviour looks a bit odd, not sure why this would just return the original item's grandparent regardless of what type it is? Code seems to be making assumptions about the structure of the course that aren't necessarily correct...