// where credit_memo is a record
var item_line_count = credit_memo.getLineCount({sublistId: 'item'});
//...
if (current_line == null || current_line == 0 ) {
                try {
                    credit_memo.removeLine({
                        sublistId: 'item',
                        line: i
                    });
                    log.debug({
                        title: 'removed line#' + i,
                        details: i
                    })
                    continue
                } catch(e) {
                    stubborn_lines.push(i)
                    log.debug({
                        title: 'error removing line#' + i,
                        details: e
                    })
                }