protected Object transformEntity(Entity entity) {
log.debug("transforming group variable...");
DJGroupVariable columnsGroupVariable = (DJGroupVariable) entity;
AbstractColumn col = columnsGroupVariable.getColumnToApplyOperation();
DJCalculation op = columnsGroupVariable.getOperation();
JRDesignExpression expression = new JRDesignExpression();
//only variables from the last registered group are important now
List groupsList = getDjd().getGroupsList();