Start-Process -ArgumentList should accept an empty array / the null collection and interpret that as "no arguments to pass"

-ArgumentList (-Args) currently requires that a non-empty array be passed, which is inconvenient in scenarios where you want to pass arguments through, whether any were specified or not, such as via $Args.

An empty array or a null collection ([System.Management.Automation.Internal.AutomationNull]::Value) should be accepted and should be interpreted as “no arguments to pass”.

Currently, passing $Args through in a function is cumbersome; imagine a function wpsh whose purpose is to invoke a Windows PowerShell window from PowerShell Core, with any arguments passed through:

function wpsh {
  # Pass all arguments through. 
  # To do this in a single Start-Process call, you need a cumbersome workaround
  # via an aux. hashtable and splatting.
  # Ideally,  
  #    Start-Process (Get-Command powershell.exe).Path -Args $Args 
  # should work directly.
  $htArgs  = if ($Args.Count) { @{ Args = $Args } } else { @{} }
  Start-Process (Get-Command powershell.exe).Path @htArgs
}

Steps to reproduce

# Or: [System.Management.Automation.Internal.AutomationNull]::Value, such as produced by `& {}`
$arguments = @()  
Start-Process code -Args $arguments

Expected behavior

code (the Visual Studio CLI, if installed) should open / activate, with no arguments being passed.

Actual behavior

Invocation fails with the following error message:

Start-Process : Cannot validate argument on parameter 'ArgumentList'.
The argument is null, empty, or an element of the argument collection contains a null value.
Supply a  collection that does not contain any null values and then try the command again.

Environment data

PowerShell Core v6.0.0-beta.5 on macOS 10.12.6
PowerShell Core v6.0.0-beta.5 on Ubuntu 16.04.3 LTS
PowerShell Core v6.0.0-beta.5 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)
Windows PowerShell v5.1.15063.483 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)

[SteveL-MSFT]

@PowerShell/powershell-committee reviewed this and agree that the change in behavior makes sense and has low risk

[mklement0]

@iSazonov: It is primarily about passing $Args through, though allowing empty arrays can also help with dynamically constructed parameter lists; I’ve added an example to the initial post, based on this real-world code.