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