private NotImplementedException addExceptionInfo(NotImplementedException inner, int sheetIndex, int rowIndex, int columnIndex) {
try {
String sheetName = _workbook.getSheetName(sheetIndex);
CellReference cr = new CellReference(sheetName, rowIndex, columnIndex, false, false);
String msg = "Error evaluating cell " + cr.formatAsString();
return new NotImplementedException(msg, inner);
} catch (Exception e) {
// avoid bombing out during exception handling
e.printStackTrace();
return inner; // preserve original exception