PowerShell .NET property access swallows exceptions

Hi folks

Recently I discovered some WTF which I would like to discuss.

$p = New-Object -TypeName System.Diagnostics.Process

then check

$p.ExitCode

returns nothing

$p.ExitCode -eq $null

returns True

Let’s check the type of ExitCode property

$p | Get-Member -Name ExitCode

returns

TypeName: System.Diagnostics.Process

Name MemberType Definition
---- ---------- ----------
ExitCode Property System.Int32 ExitCode {get;}

So we see a return type is System.Int32 which is not nullable. So ExitCode property cannot return null.

Hmm… How is that possible?

Let’s try another way

$p.get_ExitCode()

it returns

Exception calling "get_ExitCode" with "0" argument(s): "No process is associated with this object." At line:1 char:16 + $p.get_ExitCode <<<< () + CategoryInfo : NotSpecified: (:) [], MethodInvocationException + FullyQualifiedErrorId : DotNetMethodException

So clearly when you get a property which throws an exception you swallows the exception and returns $null

I did not find any PowerShell documentations that states such behavior.

The only thing I found is a similar StackOverflow question about calculated properties.

So in cases if you need to get a property and you don’t want to swallow exceptions you have to use get_Property() approach