"Object reference not set to an instance of an object" message - vb.net

Question

I keep getting window that pops up when I run a VB.NET console program I made that simply says "Object reference not set to an instance of an object." The window doesn't even say "error" or anything--the title is simply the name of the project. However...I'm assuming this is something I don't want.
I searched around a bit and found posts about similar messages but couldn't figure out how they applied to my situation.
Here is some of my code. (This program is supposed to take some data from a preformatted text file that describes the geometry of a cross section of a river and systematically enters some new geometric data to represent the riverbed being cleaned/cleared out in a certain way, and then write the new data to a new file in a similar format.)
Imports System
Imports System.IO
Imports Microsoft.VisualBasic.FileIO
Module module1
Public Sub Main()
Using sr As New StreamReader("C:\inputfile.txt")
Using outfile As New StreamWriter("C:\outputfile.txt")
Dim line As String = ""
Dim styles As Globalization.NumberStyles
styles = Globalization.NumberStyles.AllowLeadingSign Or Globalization.NumberStyles.AllowDecimalPoint
Dim stations(-1) As Double
Dim elevations(-1) As Double
Dim i As Integer = 0
Do
Try
line = sr.ReadLine()
Dim stringarray() As String = line.Split()
ReDim Preserve stations(i)
ReDim Preserve elevations(i)
stations(i) = Double.Parse(stringarray(0), styles)
elevations(i) = Double.Parse(stringarray(1), styles)
Catch ex As Exception
MsgBox(ex.Message)
End Try
i = i + 1
Loop Until line Is Nothing
Dim min As Double = elevations(0)
(some more code.....)
End Using
End Using
End Sub
End Module
I only included the first part of my code because when I put a break at the "Loop Until line Is Nothing" statement, the message didn't come up until after I went through the break, but when I put the break at the "Dim min As Double = elevations(0)" statement, the message came up before the program got to the break.
I don't really get what's wrong with my code. Anyone have any ideas?
Thanks!

Answer 1

See if this works any better:
Public Sub Main()
Dim styles As Globalization.NumberStyles = Globalization.NumberStyles.AllowLeadingSign Or Globalization.NumberStyles.AllowDecimalPoint
Dim stations As New List(Of Double)
Dim elevations As New List(Of Double)
For Each line As String in File.ReadLines("C:\inputfile.txt")
Try
Dim stringarray() As String = line.Split()
stations.Add(Double.Parse(stringarray(0), styles))
elevations.Add(Double.Parse(stringarray(1), styles))
Catch ex As Exception
MsgBox(ex.Message)
End Try
Next Line
Dim min As Double = elevations(0)
Using outfile As New StreamWriter("C:\outputfile.txt")
End Using
End Sub
Note that I moved your output file to the end... you haven't written anything yet, and so it's a good idea to wait as long as possible to open it, to keep it open for as short a time as possible.

Answer 2

The code fails after the last line has been read because the exit condition (Loop Until) doesn't know that you have reached the end of file. So another loop is started and the code tries to read an inexistent line. The last ReadLine returns Nothing, but the code tries to split it.
You could add a check before trying to split the line and jump directly to the Loop Until statement if you don't have anymore lines to read. Of course I also suggest to remove the array redim at every loop and use a more flexible List(Of Double)
Dim stations = New List(Of Double)
Dim elevations = New List(Of Double)
Do
Try
' After the last line this command returns null (Nothing in VB)
line = sr.ReadLine()
if line IsNot Nothing Then
Dim stringarray() As String = line.Split()
stations.Add(Double.Parse(stringarray(0), styles))
elevations.Add(Double.Parse(stringarray(1), styles))
End If
Catch ex As Exception
MsgBox(ex.Message)
End Try
Loop Until line Is Nothing

Answer 3

OK...I feel really dumb now...after reading through all of your answers and looking at Steve's code, I realized my code was going through the loop one last time where "line" was set as nothing at the beginning of the loop and it was still trying to add "nothing" as an element to the arrays. The key to fixing it was adding an "If line IsNot Nothing" statement before the statements adding elements to the arrays, which Steve had.
Thank you all for your answers!