When managing collaborators, the end user needs to see who they have sent invitations to, even if those invitations have not yet been accepted and the other user has not created a box account. The call to get collaborations on a file or folder returns accessible_by: null for pending collaboration requests, essentially hiding the details of the pending requests and making it impossible to display those details to a user in a custom app. This data is definitely available because this feature exists in the main Box.com interface, but has not been exposed to the APIs yet.