Handling DBNull values for DateTime

I'm converting my DataTable to generic List and as I'm converting row value to object for the list, it's giving Cast Exception. I've tried handling the DBNull using the code

if (dataRow["DateCompleted"] == DBNull.Value)
{
    dataRow["DateCompleted"] = null;
}
if (dataRow["TotalRecords"] == DBNull.Value)
{
    dataRow["TotalRecords"] = 0;
}
if (dataRow["CompanyName"] == DBNull.Value)
{
    dataRow["CompanyName"] = "";
}

but DateCompleted is not accepting the null, DBNull or empty string.

After the process, I'm making object like

DemoData demoValue = new DemoData
{
    CompanyName = dataRow["CompanyName"].ToString(),
    DateCompleted = (DateTime)dataRow["DateCompleted"],
    TotalRecords = (int)dataRow["TotalRecords"]
};

and adding the object to the list

DataList.Add(demoValue);

My list is

public List<DemoData> DataList = new List<DemoData>();

and my class is

public class DemoData
{
    public string CompanyName { get; set; }
    public DateTime DateCompleted { get; set; }
    public int TotalRecords { get; set; }
}