如何使用POI避免使用空单元格的NullPointerException？

I'm trying to get some values in my java program from an excel .xlsx file using Apache POI, but I'm having trouble because my loop encounters an empty cell sometimes, then I get a NullPointerException. How can I "test" the cell before even reading it ? Here's a piece of my code :I'm trying to get some values in my java progra