Fixes #700

Comment I wrote in the issue:

I was looking into this and I think the enum value "Centered" may be incorrect - it should be "Center".

I tried various different Excel files from different Excel versions and I was able to reproduce the issue in any file where is center any cell horizontally. If someone has a file where they have a horizontally centered cell and where this issue does not happen, I'd be interested in seeing it for further testing.

The HorizontalAlignment enum was added in c3ae45e by @ andersnm, do you know if there is a reason to use Centered here?

I tested this locally and changed the enum value to Center and added a null check -> all files open without exceptions and all tests pass.

Solution

• Changed the enum from CellStyle.Centered to CellStyle.Center
• Added a null check to not attempt to parse empty values
• Changed the logic to use Enum.TryParse() instead of Enum.Parse() to avoid unncesessary exceptions
• Added a new test for checking that the alignment values are appropriately parsed