Export-Csv cannot export hashtables with null values

### Prerequisites

- [x] Write a descriptive title.
- [x] Make sure you are able to repro it on the [latest released version](https://github.com/PowerShell/PowerShell/releases)
- [x] Search the existing issues.
- [x] Refer to the [FAQ](https://github.com/PowerShell/PowerShell/blob/master/docs/FAQ.md).
- [x] Refer to [Differences between Windows PowerShell 5.1 and PowerShell](https://learn.microsoft.com/powershell/scripting/whats-new/differences-from-windows-powershell).

### Steps to reproduce

I noticed that Export-Csv cannot export hashtables with properties that have null values, with an error "Object reference not set to an instance of an object".

### Expected behavior

```console
PS> @{'a'=$null} | Export-Csv .\test.csv; Get-Content .\test.csv
"a"
```

### Actual behavior

```console
PS> @{'a'=$null} | Export-Csv .\test.csv
Export-Csv: Object reference not set to an instance of an object.
```

### Error details

```console
Exception             :
    Type       : System.NullReferenceException
    TargetSite :
        Name          : ConvertPSObjectToCSV
        DeclaringType : [Microsoft.PowerShell.Commands.ExportCsvHelper]
        MemberType    : Method
        Module        : Microsoft.PowerShell.Commands.Utility.dll
    Message    : Object reference not set to an instance of an object.
    Source     : Microsoft.PowerShell.Commands.Utility
    HResult    : -2147467261
    StackTrace :
   at Microsoft.PowerShell.Commands.ExportCsvHelper.ConvertPSObjectToCSV(PSObject mshObject, IList`1 propertyNames)
   at Microsoft.PowerShell.Commands.ExportCsvCommand.ProcessRecord()
   at System.Management.Automation.CommandProcessor.ProcessRecord()
CategoryInfo          : NotSpecified: (:) [Export-Csv], NullReferenceException
FullyQualifiedErrorId : System.NullReferenceException,Microsoft.PowerShell.Commands.ExportCsvCommand
InvocationInfo        :
    MyCommand        : Export-Csv
    ScriptLineNumber : 1
    OffsetInLine     : 16
    HistoryId        : 53
    Line             : @{'a'=$null} | Export-Csv .\test.csv
    Statement        : Export-Csv .\test.csv
    PositionMessage  : At line:1 char:16
                       + @{'a'=$null} | Export-Csv .\test.csv
                       +                ~~~~~~~~~~~~~~~~~~~
    InvocationName   : Export-Csv
    CommandOrigin    : Internal
ScriptStackTrace      : at <ScriptBlock>, <No file>: line 1
```

### Environment data

```powershell
Name                           Value
----                           -----
PSVersion                      7.5.2
PSEdition                      Core
GitCommitId                    7.5.2
OS                             Microsoft Windows 10.0.19044
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0
```

### Visuals

_No response_

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Export-Csv cannot export hashtables with null values #25836

Prerequisites

Steps to reproduce

Expected behavior

Actual behavior

Error details

Environment data

Visuals

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

Uh oh!

Export-Csv cannot export hashtables with null values #25836

Description

Prerequisites

Steps to reproduce

Expected behavior

Actual behavior

Error details

Environment data

Visuals

Metadata

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

Issue actions