nonullallowedexception was unhandled c# (Column 'Bill Name' does not allow nulls)

private void bindingNavigatorAddNewItem_Click(object sender, EventArgs e)
       {
           if (openFileDialog1.ShowDialog() == DialogResult.OK)
           {

               FileInfo fi = new FileInfo(openFileDialog1.FileName);
               byte[] data = new byte[fi.Length];
               FileStream fs = fi.Open(FileMode.Open, FileAccess.Read, FileShare.Read);
               fs.Position = 0;
               fs.Read(data, 0, Convert.ToInt32(fi.Length));
               SqlConnection conn = new SqlConnection(string.Format("Data Source=SELVA-T;Initial Catalog=textile;Integrated Security=True"
                       , ServerName
                       , DatabaseName)
                       );

               try
               {
                   conn.Open();
                   SqlCommand cmd = new SqlCommand("INSERT INTO bill ([Bill Name],[Data],Date1) VALUES (@File,@Data, @Date)", conn);
                   cmd.Parameters.AddWithValue("@File", fi.Name);
                   cmd.Parameters.AddWithValue("@Data",data);
                   cmd.Parameters.AddWithValue("@Date", DateTime.Now);
                   cmd.ExecuteNonQuery();
                   long si;
                   si = fi.Length / 1024;
                   MessageBox.Show("u inserted the file size of " + si.ToString() + "kb");
                   textileDataSet.Tables[0].Rows.Add(fi.Name,data);
                   textileDataSet.Tables[0].AcceptChanges();
                   conn.Close();
               }
               catch (Exception r)
               {
                   MessageBox.Show(r.Message);
               }
           }


       }