CTBorder ct = getCTBorder();
if(color == null && !ct.isSetBottom()) return;
CTBorderPr pr = ct.isSetBottom() ? ct.getBottom() : ct.addNewBottom();
if(color != null) pr.setColor(color.getCTColor());
else pr.unsetColor();
int idx = _stylesSource.putBorder(new XSSFCellBorder(ct, _theme));
_cellXf.setBorderId(idx);
_cellXf.setApplyBorder(true);