Object reference not set to an instance of an object.

Imports CPSD_PDC.CalendarInterface
Public Class Form1
Dim ddd As CPSD_PDC.CPSD_PersianDateConverter
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
TextBox1.Text = ddd.PopUpCalendar(Mini, False, )
End Sub
End Class