Extension Get Status Error

[teknoskop]

Hi,Sample code where I get the extension status information.
but there is an error.

Object reference not set to an instance of an object.

private void button1_Click(object sender, EventArgs e)
{
var ext = PhoneSystem.Root.GetExtensions().FirstOrDefault(f => f.Number == "2205");

textBox2.Text = ext.UserStatus.ToString();

}