Update-ModuleManifest corrupts PrivateData in module manifest

[sdwheeler]

This bug by @jformacek is copied from MicrosoftDocs/PowerShell-Docs#6767

Usage of this command on existing module manifest breaks it's content. I wanted to use this command inside build pipeline to update ModuleVersion attribute, but found at least 2 things that got broken on my manifest module:

• RequiredAssembles attribute: I have something like below in my manifest file, and Update-ModuleManifest removes this attribute completely

RequiredAssemblies = if($PSEdition -eq 'Desktop') {@('lib\net45\someAssembly.dll')} else {$null}

• PrivateData attribute: I have added additional content as hashtable Messages to module's PrivateData as addtional hashtable aside from PSData as shown below, however, Update-ModuleManifest changes the Messages hashtable to Messages = 'System.Collections.Hashtable', which breaks the logic of module

PrivateData = @{
    Messages = @{
        NotInitialized = 'Call Initialize-Module before running other cmdlets.'
    }
    PSData = @{
    # ... standard content
    }

---

Would be great to update the command so as it does not change the attributes that are not passed from command line, or at least document here what gets changed/reset when command is run, so as users are not surprised after running it.

[sdwheeler]

After reviewing the source code, it appears that Update-ModuleManifest supports single values or arrays for extra data. See https://github.com/PowerShell/PowerShellGetv2/blob/f45bfe1a66df7063aa8de10fc4f147fdc23639af/src/PowerShellGet/private/functions/Get-PrivateData.ps1#L61-L79