Weird Object[] casting from PSObject through a function call - powershell

Question

I'm currently coding a function able to cast an ADO (EML attachments from Email) into a PSObject. A stub of the code looks like this:
function Get-OriginalMailAttributes([__ComObject]$email){
#.DESCRIPTION Downloads in Temp the attachment and open it.
# Returns PSObjectwith values.
#STEP 1: Download EML
$TEMPFILE = "..."
if($email.Attachments.Count){
$attachment=$email.Attachments|?{$_.Filename.endsWith(".eml")} | select -First 1
$fileName = $TEMPFILE + $(New-Guid | select -exp Guid) + ".eml"
$attachment.SaveAsFile($fileName)
#STEP2 : Retrieve EML Objects
$adoDbStream = New-Object -ComObject ADODB.Stream
$adoDbStream.Open()
$adoDbStream.LoadFromFile($fileName)
$cdoMessage = New-Object -ComObject CDO.Message
$cdoMessage.DataSource.OpenObject($adoDbStream, "_Stream")
#STEP 3: Bind values
$attributes = New-Object PSObject -Property #{
From = [string]($cdoMessage.Fields.Item("urn:schemas:mailheader:from").Value.toString())
}
#STEP 4: Cleanup
[System.Runtime.InteropServices.Marshal]::ReleaseComObject($cdoMessage)
[System.Runtime.InteropServices.Marshal]::ReleaseComObject($adoDbStream)
Remove-Item $fileName
return $attributes
# Note that the debugger acknowledge the fact that $attributes is PSObject.
}
}
I'm then calling the function at some point:
$sender_raw = Get-OriginalMailAttributes $email
$sender_raw.getType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True Object[] System.Array
$sender_raw
0
0
From
----
"Bob" <dummy#contoso.com>
$sender_raw.From # Crashes.
Where does this behavior come from?

Answer 1

Typically when you have "extra" values in the output from a function it's because you're calling methods that have return values and not dealing with those values.
.Add() methods are notorious for outputting the index of the item that was added.
To avoid this problem, you have a few options:
Cast to void: [void]$collection.Add($item)
Assign to $null: $null=$collection.Add($item)
Pipe to out-null: $collection.Add($item) | out-null
I don't see any obvious methods in your code, but adding Write-output 'Before Step 1' etc. throughout the code should make it clear where the offending statements are.

Answer 2

This weird behavior comes from multi-returns from PowerShell functions.
PS> function f() {
1+1
return 4
}
PS> f
2
4
In short, if one-liners are returning values, they are added as an Object[] array to the output.
While this is a particularly chaotic way to handle return values of a function, my solution on my code will be to redirect output NULL:
stub...
[System.Runtime.InteropServices.Marshal]::ReleaseComObject($cdoMessage) | Out-Null
[System.Runtime.InteropServices.Marshal]::ReleaseComObject($adoDbStream) | Out-Null
See Suppressing return values in PowerShell functions