VB.Net Excel Addin, how to write data to specific worksheet by name?

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VB

MS-Excel

AddIn

So here's the problem I have. I am converting an old Excel macro into an excel add in so I can share it easier with my coworkers. I am new to VB.net but I'm doing what I can so please go easy on me.

I have a Windows form that allows a user to enter data and when they hit the enter data button the data is supposed to go form the form to a specific worksheet. The code is as follows:

Imports Excel = Microsoft.Office.Interop.Excel

Public Class Form_CutListEntry
    'Local Dims for this Class. 
    Dim xApp As Excel.Application = GetObject(, "Excel.Application")
    Dim wb As Microsoft.Office.Tools.Excel.Workbook = xApp.ActiveWorkbook
    Dim wss As Microsoft.Office.Tools.Excel.Worksheet



    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub


    Private Sub Btn_InsertJobInfo_Click(sender As Object, e As EventArgs) Handles Btn_InsertJobInfo.Click

        wss = wb.Worksheets("Job Info")

        If Trim(TxtBx_CustomerName.Text) = "" Then
            TxtBx_CustomerName.Focus()
            MsgBox("Please enter a Customer Name")
            Exit Sub
        End If

        If Trim(TxtBx_OrderNum.Text) = "" Then
            TxtBx_OrderNum.Focus()
            MsgBox("Please enter an Order Number")
            Exit Sub
        End If

        If Trim(TxtBx_CutlistAuthor.Text) = "" Then
            TxtBx_CutlistAuthor.Focus()
            MsgBox("Please enter your initials")
            Exit Sub
        End If

'input data into spreadsheet
        wss.Cells(3, 1) = "Customer Name: " + TxtBx_CustomerName.Text
        wss.Cells(4, 1) = "Order Number: " + TxtBx_OrderNum.Text
        wss.Cells(5, 1) = "Todays Date: " + TxtBx_TodaysDate.Text
        wss.Cells(6, 1) = "Cutting List Prepared By: " + TxtBx_CutlistAuthor.Text

        Exit Sub
    End Sub

This gives me the following error when I try and run it:

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=Toms CutList Maker
  StackTrace:
       at Toms_CutList_Maker.Form_CutListEntry.Btn_InsertJobInfo_Click(Object sender, EventArgs e) in d:\tom\documents\visual studio 2013\Projects\Toms CutList Maker\Toms CutList Maker\CutList Entry.vb:line 18
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
  InnerException: 

That error is on the line :

wss = wb.Worksheets("Job Info")

I have tried changing the line to:

wss = wb.ActiveSheet

But the same error pops up. Any ideas or links to articles or anything would be appreciated.