C# : I can't set the value using in getset in spacial button

Hello all, I am getting error when I trying to set value using get set method it retun null here, and from other button it is working fine. am i missing some thing? please help

private void button7_Click(object sender, EventArgs e)
        {
             OpenFD.Title = "Select Files";
            OpenFD.Filter = "Jpg|*.jpg|Jpge|*.jpge|Gif|*.gif";
            OpenFD.FileName = null;
            string fileName;
            if (OpenFD.ShowDialog() != DialogResult.Cancel)
            {
                querybuilder qu = new querybuilder();
                fileName = OpenFD.FileName;
          // setting the value here for getset.big
                getset.big = fileName;
                Object refmissing = System.Reflection.Missing.Value;
                try
                {
                    pictureBox2.Load(fileName);
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error" + ex.Message.ToString());
                }
            }
        }

class for setting big is

class getset
{
    public static string photo;
    public static string big
    {
        get { return photo; }
        set { photo = value; }
    }
}

and when I am trying to give out put then it return null while from other button when i am trying to set the value it work fine can any one help me please

if (getset.big != null)
                {
                    // trying to displaying here
                    MessageBox.Show(getset.big);
                }
                else
                {
                    MessageBox.Show("Problem is in Image");
                }

other button code

private void button6_Click(object sender, EventArgs e)
        {
// here it has been set
            getset.big = "fddfdf";
        }

Tags: C#, .NET, Windows Forms