Object reference not set to an instance of an object.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using Volante;

namespace Dataverse
{
    public partial class fill_in_form : Form
    {
        public fill_in_form()
        {
            InitializeComponent();
        }
        public long insertedCount;
       
        public class fields_to_fill : Volante.Persistent //contains all data from student fillin form
        {
              
            //fill in form [data field] for students
              public string STU_Firstname;
              public string STU_Lastname;
              public Int64 STU_Age;
              public string STU_gender;
              public string STU_school;
              public string G_firstname;
              public string G_lastname;
              public Int64 G_contact;
              public string G_Occupation;
              public Image STU_pic;


        }
        public class databaseroot : Persistent
        {/// indexers for criteria search with volante theory
         /// the following indexers are the objects which contain the data
            public IIndex<string,> Fisrtname;
            public IIndex<string,fields_to_fill>Lastname;
            public IIndex<int64,> Age;
            public IIndex<string,> gender;
            public IIndex<string,> school;
            public IIndex<string,> G_firstname;
            public IIndex<string,> G_lastname;
            public IIndex<int64,> G_contact;
            public IIndex<string,> Occupation;
            public IIndex<Image, fields_to_fill> Stu_pic;

        
       
        }
     databaseroot DVdbrootobject = new databaseroot();

        private void fill_in_form_Load(object sender, EventArgs e)
        {
            ///open the Dataverse database created or create a new one
            IDatabase db = DatabaseFactory.CreateDatabase();
            progressBar1.PerformStep();//load the progressbar control to 100
            if (progressBar1.Maximum <= 100)
            {
                db.Open("fileinfo.dbs");
                MessageBox.Show("Database Opened", "Dataverse");
            }
            /// 
             
             if (null != db.Root)
             {
                 DVdbrootobject =  (databaseroot)db.Root;
             }
             else
             {
                 ///make root for the first time
                 ///root is inherited by all fields
                 ///root points to all fields
                 ///code in line 1 is to create a root object for firstname field 
                 DVdbrootobject = new databaseroot();
            /*1*/DVdbrootobject.Fisrtname = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.Lastname = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.Age = db.CreateIndex<int64,>(IndexType.NonUnique);
                 DVdbrootobject.gender = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.school = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.G_firstname = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.G_lastname = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.G_contact = db.CreateIndex<int64,>(IndexType.NonUnique);
                 DVdbrootobject.Occupation = db.CreateIndex<string,>(IndexType.NonUnique);
                 DVdbrootobject.Stu_pic = db.CreateIndex<Image, fields_to_fill>(IndexType.Unique);
                 db.Root = DVdbrootobject;

                 ///commit function form the volante dll , makes sure all changes are made to the file on the disk 
                 db.Commit();
                
                               
             }

        }
                
        private void button2_Click(object sender, EventArgs e)
        {
            STU_Datafill();
        }
        //fill in the database for students
        public void STU_Datafill()
        {
           ///function field of initialization
           ///SO field
                var enter = new fields_to_fill();//object of class field for oop functionality
                DVdbrootobject = new databaseroot();//Re_instantiate dataverse root object 
                 fields_to_fill givefield = new fields_to_fill();
                  FirstnameTB.Text = givefield.STU_Firstname;
                  LastnameTB.Text = givefield.STU_Lastname;
                  AgeTB.Text = givefield.STU_Age.ToString();
                  SchoolTB.Text = givefield.STU_school;
                  GfirstnameTB.Text = givefield.G_firstname;
                  GlastnameTB.Text = givefield.G_lastname;
                  GcontactTB.Text = givefield.G_contact.ToString();
                  GoccupTB.Text = givefield.G_Occupation;

            ///EO field
                 
                DVdbrootobject.Fisrtname.Put(enter.STU_Firstname, enter);
                DVdbrootobject.Lastname.Put(enter.STU_Lastname, enter);
                DVdbrootobject.Age.Put(enter.STU_Age, enter);
                DVdbrootobject.school.Put(enter.STU_school, enter);
                DVdbrootobject.G_firstname.Put(enter.G_firstname, enter);
                DVdbrootobject.G_lastname.Put(enter.G_lastname, enter);
                DVdbrootobject.G_contact.Put(enter.G_contact, enter);
                DVdbrootobject.Occupation.Put(enter.G_Occupation, enter);
                IDatabase db = DatabaseFactory.CreateDatabase();

                if (insertedCount % 10000 == 0)
                {
                    db.Commit();
                }
           
          

        }
    
    }
}