Question : linq query handling null datetime

I have a dataset with two tables. I have a linq query that is joining the tables and returning data as expected unless EndDate is null. If the date field is null I get an error
"Cannot cast DBNull.Value to type 'System.DateTime'. Please use a nullable type."

I need all rows even if EndDate is null. What is the best way to handle the null issue and get all rows of data?

var query = from xxxxx
                    where xxxxx

                     select new ReturnResult
                     {
                            LastName = person.Field("LastName"),
                            FirstName = person.Field("FirstName"),
                            StartDate = person.Field("StartDate"),                            
                            EndDate = person.Field("EndDate")
                      }

ReturnResult is a class I defined.

public class PersonnelResult
{
        public String LastName
        {get; set;}
        public String FirstName
        {get; set;}
        public DateTime StartDate
        {get; set;}
        public DateTime EndDate
        {get; set;}
}

Answer : linq query handling null datetime

make your date time variables

DateTime? yourDate;  (this is a nullabe datetime object)