ession by passing in null.  <p>

 Note also that the Properties object is used only the first time
 this method is called, when a new Session object is created.
 Subsequent calls return the Session object that was created by the
 first call, and ignore the passed Properties object.  Use the
 <code>getInstance</code> method to get a new Session object every
 time the method is called. <p>

 Additional security Permission objects may be used to
 control access to the default session. <p>

 In the current impl