Trying to open form with onclick event of a combobox on a sub-form

I am trying to open form with an onclick event of a combobox on a sub-form IF the combo-box has a value in it.

I've tried these two things but neither of them will open the form if a value is in the combo-box I am clicking on: (Note:  The value in the combobox is text).

Private Sub cboPart_No_Click()
    If Me.cboPART_NO <> "" Then
        DoCmd.OpenForm "frmPOpricing"
    End If
End Sub


Private Sub cboPart_No_Click()
    If Not IsNull(Me.cboPART_NO) Then
        DoCmd.OpenForm "frmPOpricing"
    End If
End Sub