#vulnerable code 
                             public CellStyle getOrCreateCellStyle(int x, int y) {
		final Cell cell = getOrCreateCell(x, y);
		CellStyle cellStyle = cell.getCellStyle();
		if (null == cellStyle) {
			cellStyle = this.workbook.createCellStyle();
			cell.setCellStyle(cellStyle);
		}
		return cellStyle;
	} 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public CellStyle getOrCreateCellStyle(int x, int y) {
		final CellStyle cellStyle = getOrCreateCell(x, y).getCellStyle();
		return StyleUtil.isNullOrDefaultStyle(this.workbook, cellStyle) ? createCellStyle(x, y) : cellStyle;
	}