code: public void setSessionAttributeFilter( @Nullable final String sessionAttributeFilter ) {
          if ( sessionAttributeFilter == null || sessionAttributeFilter.trim().equals("") ) {
              _sessionAttributeFilter = null;
              _sessionAttributePattern = null;
          }
          else {
              _sessionAttributeFilter = sessionAttributeFilter;
              _sessionAttributePattern = Pattern.compile( sessionAttributeFilter );
          }
      }
docs: Set the pattern used for including session attributes to a session-backup.
  If not set, all session attributes will be part of the session-backup.
  <p>
  E.g. <code>^(userName|sessionHistory)$</code>
  </p>
  
  @param sessionAttributeFilter
  the sessionAttributeNames to set