docs: public ConcurrentMap<String, Object> getAttributesFiltered() {
          if ( this.manager == null ) {
              throw new IllegalStateException( "There's no manager set." );
          }
          final Pattern pattern = ((SessionManager)manager).getMemcachedSessionService().getSessionAttributePattern();
          final ConcurrentMap<String, Object> attributes = getAttributesInternal();
          if ( pattern == null ) {
              return attributes;
          }
          final ConcurrentMap<String, Object> result = new ConcurrentHashMap<String, Object>( attributes.size() );
          for ( final Map.Entry<String, Object> entry: attributes.entrySet() ) {
              if ( pattern.matcher(entry.getKey()).matches() ) {
                  result.put( entry.getKey(), entry.getValue() );
              }
          }
          return result;
      }