.NET 4.x При streamreader.ReadLine() выскакивает ошибка object reference not set to an instance of object - C#

 
public void ReadFile()
        {
            StreamReader streamreader = new StreamReader("Exhibitions.txt");
            FileInfo file = new FileInfo("Exhibitions.txt");
            First();
            _current = 0;
            string hourformat = "t";
            string dateformat = "dd.MM.yyyy";
            while (!streamreader.EndOfStream)
            {
                _exhibitions[_current].set_name_exh(streamreader.ReadLine());
                _exhibitions[_current].set_description_exh(streamreader.ReadLine());
                _exhibitions[_current].set_category_exh(streamreader.ReadLine());
                _exhibitions[_current].set_autor_exh(streamreader.ReadLine());
                _exhibitions[_current].set_start_date_exh(DateTime.ParseExact(streamreader.ReadLine(), dateformat, System.Globalization.CultureInfo.InvariantCulture));
                _exhibitions[_current].set_end_date_exh(DateTime.ParseExact(streamreader.ReadLine(), dateformat, System.Globalization.CultureInfo.InvariantCulture));
                _exhibitions[_current].set_start_hour_exh(DateTime.ParseExact(streamreader.ReadLine(), hourformat, System.Globalization.CultureInfo.InvariantCulture));
                _exhibitions[_current].set_end_hour_exh(DateTime.ParseExact(streamreader.ReadLine(), hourformat, System.Globalization.CultureInfo.InvariantCulture));
               // out_all_result(_exhibitions[_current]);
                _current++;
            }
            streamreader.Close();
        }

 public Exhibitions()
        {
            name_exh = "";
            description_exh = "";
            category_exh = "";
            autor_exh = "";
            start_date_exh = DateTime.Now;
            end_date_exh = DateTime.Now;
            start_hour_exh = DateTime.Now;
            end_hour_exh = DateTime.Now;
        }

public Exhibitions[] _exhibitions = new Exhibitions[50];
 
//даже делал так пере запуском процедуры
 
private Exhibitions exhibitions;
 
public void arraies()
        {
            exhibitions = new Exhibitions();
            for(int i = 0;i<50;i++)
            {
                _exhibitions[i] = exhibitions;
            }
        }

public void set_name_exh(string name)
        {
            name_exh = name;
        }
        public void set_description_exh(string description)
        {
            description_exh = description;
        }
        public void set_category_exh(string category)
        {
            category_exh = category;
        }
        public void set_autor_exh(string autor)
        {
            autor_exh = autor;
        }
        public void set_start_date_exh(DateTime start_date)
        {
            start_date_exh = start_date;
        }
        public void set_end_date_exh(DateTime end_date)
        {
            end_date_exh = end_date;
        }
        public void set_start_hour_exh(DateTime start_hour)
        {
            start_hour_exh = start_hour;
        }
        public void set_end_hour_exh(DateTime end_hour)
        {
            end_hour_exh = end_hour;
        }

_exhibitions[_current].set_name_exh(streamreader.ReadLine());

public void WriteFile(string name, string description, string category, string autor, string start_date, string end_date, string start_hour, string end_hour)
        {
            StreamWriter streamwriter;
            FileInfo file = new FileInfo("Exhibitions.txt");
            streamwriter = file.AppendText();
            streamwriter.WriteLine(name);
            streamwriter.WriteLine(description);
            streamwriter.WriteLine(category);
            streamwriter.WriteLine(autor);
            streamwriter.WriteLine(start_date);
            streamwriter.WriteLine(end_date);
            streamwriter.WriteLine(start_hour);
            streamwriter.WriteLine(end_hour);
            streamwriter.Close();
        }
        
//которая вызывается вот сдесь:
 
 private void button1_Click(object sender, EventArgs e)
        {
            iter = new Exh_iter();
            string hourformat = "t";
            string dateformat = "dd.MM.yyyy";
            if ((this.textBox1.Text != "") && (this.textBox2.Text != "") &&(this.textBox3.Text != "") &&(this.textBox4.Text != "") &&(this.textBox5.Text != "") &&(this.textBox6.Text != "") &&(this.textBox7.Text != "") &&(this.richTextBox1.Text != ""))
            {
                string name = this.textBox1.Text;
                string description = this.richTextBox1.Text;
                string category = this.textBox2.Text;
                string autor = this.textBox7.Text;
                string start_date = this.textBox3.Text;
                string end_date = this.textBox4.Text;
                string start_hour = this.textBox5.Text;
                string end_hour = this.textBox6.Text;
                iter.WriteFile(name, description, category, autor, start_date, end_date, start_hour, end_hour);
                this.Hide();
                this.Close();//кстати эта функция тоже почему то не работает, но хоть ошибку не выбивает, просто не закрывает форму. ниодну.
                Form1 form1 = new Form1();
                form1.HideToolStripMenuItem();
                form1.ShowDialog(); 
            }
            else
            {
                Form6 form6 = new Form6();
                form6.ShowDialog();
            }                                    
        }