PowerShell and $null as method parameter

Question

Is PowerShell's $null equivalent to .NET's null? I have a scenario, wherein I have to invoke a .NET method from PowerShell and pass null as method parameter. As of now, I am getting some assembly loading related error on method invocation. I am wondering if $null is the culprit. Also, please share if you know what is the correct way of invoking .NET method with null parameter from PowerShell.

Method signature:

void SetUp(IKernel kernel, Action<IBindingInSyntax<object>> obj)

Thanks

The method parameter is nullable ? Could you post the method's sign? — CB.
– CB., Commented Jul 14, 2014 at 16:03
if you are in powershell version 2.0 and the param is string type try to declare the variable as [System.Management.Automation.Language.NullString]::Value — CB.
– CB., Commented Jul 14, 2014 at 16:07

Serjx86 · Accepted Answer · 2017-03-01 20:53:57Z

2

PowerShell converts it's $null to .NET's null just fine in function calls.

Proof by example.

Add-Type -TypeDefinition @"
public static class Foo
{
    public static bool IsNull(object o)
    {
        return o == null;
    }
}
"@ -Language CSharp

[Foo]::IsNull($null)

[Foo]::IsNull("string")

Output:

True
False

$null wraps a null reference to an object, and no wonder it just works, even though they are two different things.

edited Mar 1, 2017 at 20:53

answered Jul 16, 2014 at 21:22

Serjx86

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3 Comments

julealgon Over a year ago

This does not work if the type is something else other than object. In my case, it was a SecureString.

Serjx86 Over a year ago

> Object Class -- Supports all classes in the .NET class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all .NET classes; it is the root of the type hierarchy. learn.microsoft.com/en-us/dotnet/api/system.object?view=net-5.0 @julealgon, I doubt SecureString is not an Object. Maybe you should ask a question and offer an example where this does not work.

julealgon Over a year ago

SecureString is an object for sure, and I'm pretty sure it does not work there. I don't think asking another question is the way to go since it would be the same question as this one. I think this is the correct place to bring it up. Just replace object parameter on your method with SecureString (or anything other than object that is a reference type) and you should see the issue as well.

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