title: Exception when reading empty cells from Excel file
body: <p>When trying to read an Excel sheet I get an exception if some cell is empty:</p>
  
  <pre><code>Cell[] rowCells = sheet.getRow(1);
  </code></pre>
  
  <p>or</p>
  
  <pre><code>Cell cell = sheet.getCell(0,1);
  </code></pre>
  
  <p>I always get the same message:</p>
  
  <pre><code>java.lang.ArrayIndexOutOfBoundsException: 1
      at jxl.read.biff.SheetImpl.getCell(SheetImpl.java:356)
      at gui.ReadExcel.read(ReadExcel.java:45)
      at gui.GUIcontroller.chooseSaveFile(GUIcontroller.java:101)
  </code></pre>
  
  <p>What is the problem? How can I know if the cell is empty, so I won't copy its value?</p>