Problen in insert value in database using entity framework in n-tier arch

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entity-framework

I have 3 column in my table ID,Status,feedback.Id is identity,status value bydefault is false and I have to insert value of feedback using entity framework in n-tier arch.

I made 3 classes as

BO

namespace problemvisa
{
    public class Bo
    {
        private int id;

        public int Id
        {
            get { return id; }
            set { id = value; }
        }
        private string status;

        public string Status
        {
            get { return status; }
            set { status = value; }
        }
        private string feedback;

        public string Feedback
        {
            get { return feedback; }
            set { feedback = value; }
        }


2-DAL
 public class DAL
    {
        public bool insert(Bo aa)
        {
            if (aa.Equals(null))
            {
                return false;
            }
            else
            {
                using (problemEntities1 context = new problemEntities1())
                {
                    Table1 tt = new Table1();
                     context.AddToTable1(tt);
                     context.SaveChanges();
                }
                return true;



3.BAL


 public class BAL
    {
        public bool insert(Bo ss)
        {
            DAL dd = new DAL();
            if (dd.insert(ss))
            {
                return true;
            }
            else
            {
                return false;
            }
        }


IN aspx form



 protected void Button1_Click(object sender, EventArgs e)
        {
            
            Bo aa = new Bo();
            aa.Status = "false";
            aa.Feedback = TextBox1.Text;
            BAL ss = new BAL();
            ss.insert(aa);
        }
    }



One error is coming i.e.Cannot insert the value NULL into column 'feedback', table 'problem.dbo.Table1'; column does not allow nulls. INSERT fails.
The statement has been terminated.