According to the error the column isn't empty it's NULL - it's not the same...
Your problem is that you try to convert NULL to int which is not nullable type...
You have a few options
1. In SQL do ISNULL(column, 0) - or any other default value
2. In the code do if(Convert.IsDBNull(column)){initialize with some default value} -
http://msdn.microsoft.com/en-us/library/system.convert.isdbnull.aspx[
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3. You may use nullable int in your code -
http://msdn.microsoft.com/en-us/library/2cf62fcy.aspx[
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