Called when a Map previously returned by getPreferencesMap()
is no longer needed.
A call to finish() is not guaranteed to occur for every Map
returned by getPreferencesMap(). If an error occurs when processing a
request, the portal may not have an opportunity to call finish().
Return a map of preferences. Implementing classes use the information
available from request to determine the identity
of the user.
a Map of preference names to values, or null if no preferencesare available.