Problem with null value in my if statement

Hey there guys.  Any help here would be appreciated.  When the compiler gets to sid =  dv.Table.Rows[0][4].ToString(); it chokes if the data does not exists.  How do I get C# to not freak out when it sees a null value.  Thanks ahead of time :).  Here is the code:
protected void Page_Load(object sender, EventArgs e)
        {         
            CheckReorderStatus();
        }

        protected void CheckReorderStatus()
        {
            
            DataView dv = (DataView)SqlDataSource1.Select(DataSourceSelectArguments.Empty);


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