SheetHandler类中addNullCell方法换行时未考虑第一列数据为空导致首列数据无法赋值为空，改动如下：
private void addNullCell(String prevLocation, String currentLocation) {
String[] prev = this.getRowCell(prevLocation);
String[] current = this.getRowCell(currentLocation);
int prevCell = 1;
int currentCell = true;
int currentCell;
if (prev[1].equalsIgnoreCase(current[1])) {
prevCell = this.getCellNum(prev[0]) + 1;
currentCell = this.getCellNum(current[0]);
} else {
currentCell = this.getCellNum(current[0]);
}

    for(int i = prevCell; i < currentCell; ++i) {
        this.rowList.add(this.curCol, new SaxReadCellEntity(CellValueType.String, ""));
        ++this.curCol;
    }

}![输入图片说明](https://images.gitee.com/uploads/images/2021/0107/222526_6c8f4609_1935066.jpeg "2D89EEF6-528C-4259-A1C3-11209229EDD8.jpg")