Assigning NULL to Int and DateTime datatype

public class BrdMeeting
    {
	public int ProcessPk { get; set; }       // cannot assign NULL to Processpk.

        public int? MeetingPk{get;set;}          // can assign NULL to MeetingPk.

        public DateTime? MeetingDate{get;set;}   // can assign NULL to MeetingDate.
       
    }