如何在创建新的Excel文件时初始化单元格（Apache POI）

I am currently using Apache POI to create empty excel files (that I will later read and edit). The problem is that whenever I try to get the cell, I always get a null value. I have tried initializing the first few columns and rows (the cells are no longer null) but with this approach, I cannot insert new rows and columns. How can I be able to initialize all cells of a sheet without having to set the number of rows and columns? ThanksI am currently using Apache POI to create empty