It is possible that a project has no supervisor attached. This occurs in two situations:
Orphan projects cannot be undertaken by students, i.e. they cannot be assigned to some student(s) regardless whether the author of such a project is a student or a lecturer. However, after a lecturer has taken over ("adopted") such a project, it is free for students to undertake.
Orphan projects are shown with pink background.
Any lecturer can take over any orphan project as supervisor. To do so, bring up the detailed single project view and select Change Engagements->Lecturers->Become Supervisor. This will turn the project into the exact same category as any other project which is supervised by that lecturer. This step does not assign any student to the project.
There are multiple reasons why taking over an orphan project and assigning students to such a project are two separate steps. For instance: