ReadKey null reference exception

[veleek]

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues, especially the pinned issues.

Exception report

### Environment
PSReadLine: 2.2.6
PowerShell: 7.3.6
OS: Microsoft Windows 10.0.19045
BufferWidth: 200
BufferHeight: 60

Last 8 Keys:

 c l s Enter
 UpArrow UpArrow UpArrow Enter


### Exception

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.PowerShell.PSConsoleReadLine.ReadKey()
   at Microsoft.PowerShell.PSConsoleReadLine.InputLoop()
   at Microsoft.PowerShell.PSConsoleReadLine.ReadLine(Runspace runspace, EngineIntrinsics engineIntrinsics, CancellationToken cancellationToken, Nullable`1 lastRunStatus)

Screenshot

N/A

Environment data

PS Version: 7.3.6
PS HostName: ConsoleHost (Windows Terminal)
PSReadLine Version: 2.2.6
PSReadLine EditMode: Windows
OS: 10.0.19041.1 (WinBuild.160101.0800)
BufferWidth: 280
BufferHeight: 71

Steps to reproduce

I have a long running script that uses a FileSystemWatcher to monitor for changes to a file.
I had a bug where I didn't set the source identifier before registering for events, like so:

$watcher = [System.IO.FileSystemWatcher]::new($logPath, $logFilter)
Register-ObjectEvent $watcher Created -SourceIdentifier $createdEventIdentifier

# Later on in function
$createdEventIdentifier = "Blah"

So I accidentally created a registeration without an event handler, then later on in a try/finally I did:

Unregister-Event -SourceIdentifier $createdEventIdentifier -ErrorAction "SilentlyContinue"

So the unregisteration wouldn't do anything.

The end result was that when I kill my function (with Ctrl+C), I get into a NullReferenceException loop. I'm still able to input text, but it just repeatedly dumps the exceptions shown above.

If I run Get-EventSubscriber | Unregister-Event (yes I can still successfully run commands while it's in this error loop), then the erroring stops.

Expected behavior

Existing event subscriptions should not cause problems with ReadKey.

Actual behavior

ReadKey returns exceptions repeatedly until event registration is removed.

[veleek]

I was able to reproduce this with this minimial function:

function test() {
    $watcher = [System.IO.FileSystemWatcher]::new("C:\", "*.log")
    Register-ObjectEvent $watcher Created -SourceIdentifier $null
}

Run the test function and see the error loop. Passing any non $null value (including empty string "")for SourceIdentifier works properly.

[veleek]

@daxian-dbw - Amazing turnaround! Thanks!