Merge pull request OfficeDev#32 from leocui9387/patch-1

Line 419: Null Reference Exception on empty cells

Author: lindalu-MSFT

docs/how-to-retrieve-the-values-of-cells-in-a-spreadsheet.md

@@ -416,7 +416,7 @@ code sample in C\# and Visual Basic.
               Where(c => c.CellReference == addressName).FirstOrDefault();
 
             // If the cell does not exist, return an empty string.
-            if (theCell != null)
+            if (theCell.InnerText.Length > 0)
             {
                 value = theCell.InnerText;