title: XSSF saving workbook
body: <p>I am using XSSF to create a workbook and continually getting this error:</p>
  
  <p>Excel found unreadable content in 'thefile'.xlsx. Do you want to recover the contents of this workbook? If you trust the source of the workbook click Yes.
  Excel then obligingly recovers it by removing all of the data and gives the detail error report:
  Removed Records: Cell information from /xl/worksheets/sheet1.xml part</p>
  
  <p>I am following these principles:
  Ensure the row is created and not null.
  Ensure the cell is created and not null.
  Ensure the cell is the correct type.
  Write to cell.</p>
  
  <p>Is there something I am missing, eg is it permissable to have only certain cells written to in a row eg:</p>
  
  <p>|null|null|write something here|null|null|</p>
  
  <p>and the same with rows:</p>
  
  <hr>
  
  <p>row with content</p>
  
  <hr>
  
  <p>null</p>
  
  <hr>
  
  <p>row with content</p>
  
  <hr>
  
  <p>or do I need to ensure the all rows and columns are filled blank through the ranges used.
  This is a complete mystery.</p>