Access the close time after which this assignment can no longer be viewed, and after which submissions will not be accepted. May be null.
The Time after which the Assignment is closed, or null if unspecified.
Access the drop dead time after which responses to this assignment are considered late; may be null.
The Time object representing the drop dead time, or null if unspecified.
Access the groups defined for this assignment.
A Collection (String) of group refs (authorization group ids) defined for this message; empty if none are defined.