Any attempt to Show help for the parameter at the cursor (Alt-H) causes exception on Windows PowerShell 5.1

[kMitty]

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: 2.3.6+d2e770f93b7a53d8660a6402eb29d1ae1c35e767
PowerShell: 5.1.14409.1029
OS: Microsoft Windows 6.3.9600
BufferWidth: 120
BufferHeight: 3000

Last 200 Keys:

 Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+Pa
geDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown P
ageDown Ctrl+Alt+/ Backspace Ctrl+Alt+/ Backspace / Backspace Ctrl+Alt+? PageUp Shift+PageDown Shift+PageDown Shift+Page
Down Shift+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ct
rl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageD
own Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl
+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDow
n Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+P
ageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown
Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+Pag
eDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ct
rl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown Ctrl+PageDown PageDown Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+Pa
geUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+Pa
geUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+Pa
geUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+Pa
geUp UpArrow UpArrow Ctrl+a RightArrow Alt+a Alt+a RightArrow Alt+a RightArrow RightArrow RightArrow RightArrow RightArr
ow RightArrow RightArrow RightArrow RightArrow Alt+a RightArrow RightArrow RightArrow RightArrow RightArrow RightArrow R
ightArrow RightArrow RightArrow Escape Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+Page
Up Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp Ctrl+Page
Up Ctrl+PageUp Ctrl+PageUp Ctrl+PageUp g e t - c o m Tab F1 Spacebar Spacebar - Tab Tab Alt+h

### Exception

Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: Cannot perform runtime binding on a null reference
   at CallSite.Target(Closure , CallSite , Object )
   at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0)
   at Microsoft.PowerShell.PSConsoleReadLine.WriteParameterHelp(Object helpContent)
   at Microsoft.PowerShell.PSConsoleReadLine.WriteDynamicHelpContent(String commandName, String parameterName, Boolean i
sFullHelp)
   at Microsoft.PowerShell.PSConsoleReadLine.ProcessOneKey(PSKeyInfo key, Dictionary`2 dispatchTable, Boolean ignoreIfNo
Action, Object arg)
   at Microsoft.PowerShell.PSConsoleReadLine.InputLoop()
   at Microsoft.PowerShell.PSConsoleReadLine.ReadLine(Runspace runspace, EngineIntrinsics engineIntrinsics, Cancellation
Token cancellationToken, Nullable`1 lastRunStatus)

Screenshot

Environment data

PS Version: 5.1.14409.1029
PS HostName: ConsoleHost
PSReadLine Version: 2.3.6
PSReadLine EditMode: Windows
OS: 6.3.9600.16384 (winblue_rtm.130821-1623)
BufferWidth: 120
BufferHeight: 3000

Steps to reproduce

Start by entering any valid PS cmdlet, then '-' (dash), 'Tab' for completion, Alt-H

Expected behavior

Get help for the parameter at the cursor.

Actual behavior

The above exception happens

[kborowinski]

@daxian-dbw It happens also on PowerShell 7.5.3 and 7.6.0-preview.5 but for some cmdlets only, like Get-ADComputer:

PS C:\> Get-ADComputer -ResultPageSize
Oops, something went wrong.
Please report this bug with ALL the details below, including both the 'Environment' and 'Exception' sections.
Please report on GitHub: https://github.com/PowerShell/PSReadLine/issues/new?template=Bug_Report.yaml
Thank you!

### Environment
PSReadLine: 2.4.4-beta4
PowerShell: 7.5.3
OS: Microsoft Windows 10.0.26200
BufferWidth: 188
BufferHeight: 53

Last 44 Keys:

 C : Enter
 g e t - a d c Tab Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace Backspace d c Tab Tab Tab Tab Tab Spacebar - r e Tab Alt+h

### Exception

Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: Cannot perform runtime binding on a null reference
   at CallSite.Target(Closure, CallSite, Object)
   at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0)
   at Microsoft.PowerShell.PSConsoleReadLine.WriteParameterHelp(Object helpContent)
   at Microsoft.PowerShell.PSConsoleReadLine.WriteDynamicHelpContent(String commandName, String parameterName, Boolean isFullHelp)
   at Microsoft.PowerShell.PSConsoleReadLine.DynamicHelpImpl(Boolean isFullHelp)
   at Microsoft.PowerShell.PSConsoleReadLine.ShowParameterHelp(Nullable`1 key, Object arg)
   at Microsoft.PowerShell.PSConsoleReadLine.ProcessOneKey(PSKeyInfo key, Dictionary`2 dispatchTable, Boolean ignoreIfNoAction, Object arg)
   at Microsoft.PowerShell.PSConsoleReadLine.InputLoop()
   at Microsoft.PowerShell.PSConsoleReadLine.ReadLine(Runspace runspace, EngineIntrinsics engineIntrinsics, CancellationToken cancellationToken, Nullable`1 lastRunStatus)

[daxian-dbw]

@kborowinski I don't have Get-ADComputer available on my machine. Could you please try the changes in #4971? You can get the produced artifact at https://ci.appveyor.com/project/SteveL-MSFT/psreadline/builds/52913950/artifacts

If the exception is gone, please also show me the screenshot of the printed-out help content. Thanks!

[kborowinski]

@daxian-dbw It seems that this version fixes the issue:

1. PowerShell 5.1

2. PowerShell 7.5.3

3. PowerShell 7.6.0-preview.5

[daxian-dbw]

@kborowinski Thank you!
But I'm still not sure if the fix actually works. I was assuming helpContent.type returns null, and thus helpContent.type.name caused the null reference issue. But in that case, The printed-out help content should be -ResultPageSize <> without the type name Int32.

string syntax = $"-{helpContent.name} <{helpContent.type.name}>";

Could you please try again with the original v2.4.4-beta4 PSReadLine, and see if it still reproduce? (I wonder if you ran Update-Help and fixed the help content)

[kborowinski]

@daxian-dbw :

It's fixed, and I did run Update-Help in previous tests 😅

1. PowerShell 5.1 with PSReadLine 2.4.4-beta.4:

1. PowerShell 5.1 with PSReadLine artifact:

[daxian-dbw]

@kborowinski Thank you! I appreciate your help.