code: public static PageFlowStack get( HttpServletRequest request, ServletContext servletContext )
      {
          return get( request, servletContext, true );
      }
docs: Get the stack of nested page flows for the current user session.  Create and store an empty
  stack if none exists.
  
  @param request the current HttpServletRequest.
  @param servletContext the current ServletContext.
  @return the stack of nested page flows {@link PushedPageFlow}s) for the current user session.