StreamWriter cannot call a method on a null-valued expression - nullpointerexception

Question

First time user, looking for help with a script that's been driving me crazy.
Basically, I need to create a set number of files of an exact size (512KB, 2MB, 1GB) to test a SAN. These files need to be filled with random text so that the SAN doesn't catch the nuls and does actually allocate the blocks - that's also the reason I couldn't just use fsutils.
Now, I've been messing with the new-bigrandomfile by Verboon and tweaking it to my needs.
However I'm getting the error:
You cannot call a method on a null-valued expression.
At L:\random5.ps1:34 char:9
+ $stream.Write($longstring)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
This is the bit of code I've come up with so far; I'll add a loop at the end to copy the file I just created N times so to fill up the lun.
Set-Strictmode -Version 2.0
#temp file
$file = "c:\temp\temp.rnd"
#charset size
$charset = 64
#Block Size
$blocksize = 512
#page size
$Pagesize = 512KB
#Number of blocks in a page
$blocknum = $Pagesize / $blocksize
#Resulting/desired test file size
$filesize = 1GB
#number of pages in a file
$pagenum = $filesize / $Pagesize
# create the stream writer
$stream = System.IO.StreamWriter $file
# get a 64 element Char[]; I added the - and _ to have 64 chars
[char[]]$chars = 'azertyuiopqsdfghjklmwxcvbnAZERTYUIOPQSDFGHJKLMWXCVBN0123456789-_'
1..$Pagenum | ForEach-Object {
# get a page's worth of blocks
1..$blocknum| ForEach-Object {
# randomize all chars and...
$rndChars = $chars | Get-Random -Count $chars.Count
# ...join them in a string
$string = -join $rndChars
# repeat random string N times to get a full block string length
$longstring = $string * ($blocksize / $charset)
# write 1 block to file
$stream.Write($longstring)
# release resources by clearing string variables
Clear-Variable string, longstring
}
}
$stream.Close()
$stream.Dispose()
# release resources through garbage collection
[GC]::Collect()
$file.Close()
I've tried a gazillion variants like:
$stream = [System.IO.StreamWriter] $file
$stream = System.IO.StreamWriter $file
$stream = NewObject System.IO.StreamWriter $file
Of course, being a total noob at powershell, I've tried using quotes, brackets, provided the full path instead of the variable, etc. All (or most) seem to be valid syntax variants, according to a ton of examples I found online, but the output is still the same.
In case you have any improvement to suggest or alternative way to perform this task I'm all ears.
Edited the script above: just a couple of " for $file made the error disappear, - thanks LinuxDisciple; however, the file gets created but stays at 0 bytes and the script stuck in a loop.

Answer 1

Fix your instantiation of StreamWriter to any of these correct variants:
$stream = [System.IO.StreamWriter]::new($file)
$stream = [IO.StreamWriter]::new($file) # the default namespace may be omitted
$stream = New-Object System.IO.StreamWriter $file
You can specify encoding:
$stream = [IO.StreamWriter]::new(
$file,
$false, # don't append
[Text.Encoding]::ASCII
)
See StreamWriter on MSDN for available constructors and parameters.
PowerShell ISE offers autocomplete with tooltips:
type [streamw and press Ctrl-Space to autocomplete the full .NET class name
type ]:: to see the available methods and properties
type new and press Ctrl-Space to see the constructor overrides
whenever needed, put the caret at the method name and press Ctrl-Space for the tooltip

Answer 2

I know nothing about powershell but a few things:
Are you sure $longstring has a value before you call stream.Write()? It sounds like it's null and that's why the error. If you can somehow output the value of $longstring to the console, it would help you make sure that it has a value.
Also, troubleshoot the code with a simplified version of your code, so that you can pinpoint what's going on, for example
$file = c:\temp\temp.rnd
$stream = System.IO.StreamWriter $file
$longstring = 'whatever'
$stream.Write($longstring)