Failing to parse formatting.
*Created originally on Bitbucket by [StephenGore](https://bitbucket.org/%7Bd659ccaa-d11c-47ed-882a-a03838d00153%7D/)*
I have recently attempted to open a worksheet and an error occurred in the content property of "Cell\Text.py". The error is "TypeError: sequence item 3: expected str instance, NoneType found". After taking a look in the sharedstrings.xml I found the error happened when parsing the following XML.
```
#!XML
<si>
<r>
<t>“Replaced Data”</t>
</r>
<r>
<rPr>
<sz val="11"/>
<color rgb="FF008080"/>
<rFont val="Calibri"/>
<family val="2"/>
<scheme val="minor"/>
</rPr>
<t/>
</r>
</si>
```
I think it is to do with the "<t/>" tag and not finding any data.
More information at http://stackoverflow.com/questions/34094049/failing-to-open-spreadsheet/
issue