The Agile framework called Scrum defines three roles -- Product Owner, ScrumMaster and Development Team. Nowhere in the authoritative definition of Scrum, "The Scrum Guide", authored by Jeff Sutherland and Ken Schwaber, is there mention of a role, title, or person called a project manager. In fact, there is just one mention of the word "project" and that is in reference to a Sprint. The word "manager" doesn't appear even once. What is a project manager to do then in the context of Scrum?