default UIColumn findColumn(String columnKey) {
        if ("globalFilter".equals(columnKey)) {
            return null;
        }

        List<UIColumn> columns = getColumns();

        //body columns
        for (int i = 0; i < columns.size(); i++) {
            UIColumn column = columns.get(i);
            if (Objects.equals(column.getColumnKey(), columnKey)) {
                return column;
            }
        }

        //header columns
        if (getFrozenColumnsCount() > 0) {
            UIColumn column = findColumnInGroup(columnKey, getColumnGroup("frozenHeader"));
            if (column == null) {
                column = findColumnInGroup(columnKey, getColumnGroup("scrollableHeader"));
            }

            if (column != null) {
                return column;
            }
        }
        else {
            return findColumnInGroup(columnKey, getColumnGroup("header"));
        }

        throw new FacesException("Cannot find column with key: " + columnKey);
    }
Return each {@link Row} in a Column Group.
@param context  the {@link FacesContext}
@param cg the {@link ColumnGroup} to get
@param skipUnrendered If unrendered components should be skipped
@param callback The callback, which will be invoked for each row. If it returns false, the algorithm will be cancelled
@return false when the algorithm was cancelled
primefaces/src/main/java/org/primefaces/component/api/ColumnAware.java