Subclass implementation hook that retrieves the Session object from the underlying EIS or {@code null} if a
session with that ID could not be found.
@param sessionId the id of the <tt>Session</tt> to retrieve.
@return the Session in the EIS identified by <tt>sessionId</tt> or {@code null} if a
session with that ID could not be found.
Subclass implementation hook that retrieves the Session object from the underlying EIS or {@code null} if a session with that ID could not be found.
@param sessionId the id of the <tt>Session</tt> to retrieve. @return the Session in the EIS identified by <tt>sessionId</tt> or {@code null} if a session with that ID could not be found.