@abstractmethod<EOL><INDENT>def get_session(self, create=None):<DEDENT>
pass<EOL>
Returns the application Session associated with this Subject based on
the following criteria:
    - If there is already an existing Session associated with this
      Subject, it is returned and the create argument is ignored.
    - If no Session exists and create is True, a new Session is created,
      associated with this Subject and then returned.
    - If no Session exists and create is False, None is returned.

:returns: the application Session associated with this Subject