Output custom object with headers when no values are present by jshigetomi · Pull Request #25096 · PowerShell/PowerShell

jshigetomi · Feb 26, 2025

PR Summary

This pull request includes changes to improve the handling of empty and null values in the ConvertFrom-Csv command and updates the corresponding unit tests to verify the new behavior. The most important changes include modifying the Import method in CsvCommands.cs and adding new unit tests in ConvertFrom-Csv.Tests.ps1.

Enhancements to ConvertFrom-Csv command:

src/Microsoft.PowerShell.Commands.Utility/commands/utility/CsvCommands.cs: Updated the Import method to skip empty lines only when using Import-CSV, but to keep them when using ConvertFromCSV.

Unit tests updates:

test/powershell/Modules/Microsoft.PowerShell.Utility/ConvertFrom-Csv.Tests.ps1: Added new unit tests to verify that ConvertFrom-Csv handles empty and null values correctly.

PR Context

Improve CSV parsing edge case handling and add comprehensive unit tests

PR Checklist

…wershell into fixNoValueCSVInput

jshigetomi · Feb 26, 2025

I've adjusted the behavior of ConvertFrom-CSV according to the discussion on issue #24698. Essentially I removed the feature that skips blank lines in the Import method in ImportCsvHelper. It still keeps the last cell null so as to keep this from being a breaking change. #17702

surfingoldelephant · Feb 27, 2025

+                if (values.Count == 1 && string.IsNullOrEmpty(values[0]) && !(_cmdlet is ConvertFromCsvCommand))
                {
-                    // skip the blank lines
+                    // Skip empty lines when Import-CSV but keep empty lines when ConvertFromCSV


The bug (#24698) affects both ConvertFrom-Csv and Import-Csv; I think the fix should be applied to both commands for consistency. ConvertFrom-Csv was used throughout the original issue for demonstration purposes only.

Do we know if there's a specific reason why the check for values.Count == 1 && string.IsNullOrEmpty(values[0]) was included in the first place?

This comes from Windows PowerShell.

When I disable it for Import-CSV as well, `n's are captured as an extra element. Is this the behavior we want?

Describe "Import-Csv with different newlines" -Tags "CI" { It "Test import-csv with '<name>' newline" -TestCases @( @{ name = "CR"; newline = "`r" } @{ name = "LF"; newline = "`n" } @{ name = "CRLF"; newline = "`r`n" } ) { param($newline) $csvFile = Join-Path $TestDrive -ChildPath $((New-Guid).Guid) $delimiter = ',' "h1,h2,h3$($newline)11,12,13$($newline)21,22,23$($newline)" | Out-File -FilePath $csvFile $returnObject = Import-Csv -Path $csvFile -Delimiter $delimiter $returnObject.Count | Should -Be 2 $returnObject[0].h1 | Should -Be 11 $returnObject[0].h2 | Should -Be 12 $returnObject[0].h3 | Should -Be 13 $returnObject[1].h1 | Should -Be 21 $returnObject[1].h2 | Should -Be 22 $returnObject[1].h3 | Should -Be 23 } }

Is this the behavior we want?

No, it isn't.

This is more about ensuring whatever fix is chosen for #24698 is applied to both ConvertFrom-Csv and Import-Csv. In other words, the example CSV data below should deserialize consistently, irrespective of the source being a file or a string.

"P1" "" "" ""

Can #24698 be fixed for both commands without introducing the newline issue?

I'm thinking it can be deserialized consistently but would result in just one empty string value per header.
For example,

"P1" "" "" "" # Would produce [pscustomobject] @{ P1 = '' } ignoring the other empty cells

@' "P1","P2" "", "", '@ | ConvertFrom-Csv # Would produce [pscustomobject] @{ P1 = ''; P2 = '' } ignoring the other empty cells again

This way we can produce a header only output consistently.

Thoughts?

That's not what I had in mind when I filed the issue. For each non-empty line in input data, an object should be emitted by ConvertFrom-Csv/Import-Csv.

The following (using either command) produces 3 objects:

@' "P1" "a" "b" "c" '@ | ConvertFrom-Csv

Therefore, the following (using either command) should also produce 3 objects:

@' "P1" "" "" "" '@ | ConvertFrom-Csv

Likewise, this produces 2 objects, because the empty line is correctly ignored:

@' "P1" "a" "c" '@ | ConvertFrom-Csv

Therefore, this should also produce 2 objects:

@' "P1" "" "" '@ | ConvertFrom-Csv

iSazonov · Feb 28, 2025

@jshigetomi Root of the issue in ParseNextRecord method. It does not distinguish between an input string without characters and a string with two double quotes "".

PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/CsvCommands.cs

Lines 1609 to 1613 in bfdc498

    
           result.Add(current.ToString()); 
        
           current.Remove(0, current.Length); 
        
           // New line outside quote is end of word and end of record 
        
           break;

Here current.ToString() returns string.Empty for these two cases. We can check current.Length > 0 before call ToString(). I suggest the fix (with removing

PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/CsvCommands.cs

Lines 1390 to 1394 in bfdc498

    
           if (values.Count == 1 && string.IsNullOrEmpty(values[0]) && !(_cmdlet is ConvertFromCsvCommand)) 
        
           { 
        
               // Skip empty lines when Import-CSV but keep empty lines when ConvertFromCSV 
        
               continue; 
        
           }

)

But we get to Zugzwang - sometimes we want to, sometimes we don't. Of course, it would be possible to add more conditions, but this would require a more significant code change in same methods. My suggestion is not to complicate the code. If there are concerns, then make this change an experimental feature.

iSazonov · Mar 1, 2025

@jshigetomi I checked my guess. I had to make a few more changes. You can see the result here:

master...iSazonov:PowerShell:csvblank

jshigetomi · Mar 3, 2025

@iSazonov I'm seeing test failure for Import-CSV

Maybe a warning to the user would be better for no value csvs?

iSazonov · Mar 3, 2025

I don't see errors in my branch.

jshigetomi · Mar 3, 2025

Hmm I'm having some trouble reproducing your results.

master...iSazonov:PowerShell:csvblank#diff-2b77454e7d234e46e6ebdb6c1be4ac0cb9c02b88bbe0e61c9acdfa3f66491e81R1383-R1390

How are you resolving the brackets here?

iSazonov · Mar 4, 2025

@jshigetomi Please look #25120

jshigetomi · Mar 6, 2025

/azp run

azure-pipelines · Mar 6, 2025

Azure Pipelines successfully started running 2 pipeline(s).

surfingoldelephant

I think we also need to take a look at no detected delimiter scenarios.

# Detected delimiter:

@'
P1,P2,P3
A1,,
B1,,
C1,,
'@ | ConvertFrom-Csv

# Current/expected behavior:
[pscustomobject] @{ P1 = 'A1'; P2 = ''; P3 = '' }
[pscustomobject] @{ P1 = 'B1'; P2 = ''; P3 = '' }
[pscustomobject] @{ P1 = 'C1'; P2 = ''; P3 = $null }

# No detected delimiter:

@'
P1,P2,P3
A1
B1
C1
'@ | ConvertFrom-Csv

# Current/expected behavior:
[pscustomobject] @{ P1 = 'A1'; P2 = $null; P3 = $null }
[pscustomobject] @{ P1 = 'B1'; P2 = $null; P3 = $null }
[pscustomobject] @{ P1 = 'C1'; P2 = $null; P3 = $null }


@'
P1;P2;P3
A1
B1
C1
'@ | ConvertFrom-Csv -Delimiter ';'

# Current/expected behavior:
[pscustomobject] @{ P1 = 'A1'; P2 = $null; P3 = $null }
[pscustomobject] @{ P1 = 'B1'; P2 = $null; P3 = $null }
[pscustomobject] @{ P1 = 'C1'; P2 = $null; P3 = $null }

Notice when there is no (detected) delimiter, the resultant value is always $null. Can we add tests for this?

…wershell into fixNoValueCSVInput

jshigetomi · Aug 27, 2025

/azp run

azure-pipelines · Aug 27, 2025

Azure Pipelines successfully started running 1 pipeline(s).

jshigetomi · Sep 29, 2025

/azp run PowerShell-Windows-Packaging-CI, PowerShell-CI-linux-packaging

azure-pipelines · Sep 29, 2025

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

Copilot

Pull request overview

This pull request improves the handling of empty and null values in CSV parsing commands (Import-Csv and ConvertFrom-Csv). The changes ensure that both cmdlets properly distinguish between truly empty lines (which should be skipped) and lines containing only delimiters (which represent rows with empty field values and should be processed).

Changes:

Improved logic for detecting and handling blank lines in CSV parsing
Added comprehensive test coverage for edge cases involving empty fields, null values, and various delimiter scenarios
Refactored existing tests to reduce duplication and improve maintainability
Fixed a spelling error in a test variable name

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Microsoft.PowerShell.Commands.Utility/commands/utility/CsvCommands.cs	Updated Import method to correctly identify blank lines (values.Count == 0) instead of incorrectly treating single empty strings as blank lines. Changed ParseNextRecord to return instead of break for clarity and added logic to prevent empty results from being added at the start of records. Changed loop condition from while(true) to while(!EOF) for clarity.
test/powershell/Modules/Microsoft.PowerShell.Utility/Import-Csv.Tests.ps1	Fixed spelling of variable name (emptyValueCsv). Refactored duplicate test cases into a single loop-based test for better maintainability. Added extensive new test coverage for empty/null value handling across multiple contexts: empty CSV fields, header-only scenarios, empty input with -Header parameter, edge cases with whitespace and special characters, type information handling, delimiter edge cases, and large data scenarios.
test/powershell/Modules/Microsoft.PowerShell.Utility/ConvertFrom-Csv.Tests.ps1	Added comprehensive test coverage matching the Import-Csv tests, covering the same edge cases but using ConvertFrom-Csv instead of Import-Csv, ensuring both cmdlets handle empty and null values consistently.

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…om-Csv.Tests.ps1 Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Justin Chung and others added 9 commits February 26, 2025 10:26

Output custom object with headers when no values are present

df47ac8

Merge branch 'master' into fixNoValueCSVInput

4ccc9ad

Remove if statement that skips blank lines

ba25fa7

Merge branch 'master' into fixNoValueCSVInput

7ef2c8b

Only remove the if statement for ConvertFrom-CSV

83a53ef

Merge branch 'fixNoValueCSVInput' of https://github.com/powershell/po…

b7f491d

…wershell into fixNoValueCSVInput

Add test for testing null values and empty string values

3786536

Add comment about skiping lines

50db112

Delete trailing whitespace

c4950da

PowerShell deleted a comment from azure-pipelines Bot Feb 26, 2025

jshigetomi mentioned this pull request Feb 26, 2025

CSV deserialization outputs nothing if there are only a certain number of empty fields #24698

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5 tasks

Add more test cases for empty and null values

472c6d0

PowerShell deleted a comment from azure-pipelines Bot Feb 26, 2025

Fix test to make it pester 4.10 compatible

bfdc498

surfingoldelephant reviewed Feb 27, 2025

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Add iSazonov's changes

64e6de8

Justin Chung added 2 commits March 6, 2025 11:33

Remove skip no values check and add skip blank check

8dd4a66

Revert to private feed

6c2c6c7

PowerShell deleted a comment from azure-pipelines Bot Mar 6, 2025

surfingoldelephant reviewed Mar 31, 2025

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Added tests for edge cases and updated old test for Context and typo

6e3fa23

jshigetomi requested review from iSazonov and surfingoldelephant August 4, 2025 18:32

jshigetomi added 6 commits August 4, 2025 14:20

adjust import-csv tests

de52856

Adjust ConvertFrom csv tests

87c5def

fix header param test

1ba4e61

Merge branch 'master' into fixNoValueCSVInput

7a24009

Clean up comments

effd7b2

Merge branch 'fixNoValueCSVInput' of https://github.com/powershell/po…

5bd8b40

…wershell into fixNoValueCSVInput

Merge branch 'master' into fixNoValueCSVInput

db0bbea

jshigetomi added 2 commits September 2, 2025 11:49

Merge branch 'master' into fixNoValueCSVInput

f693967

Merge branch 'master' into fixNoValueCSVInput

0b22c87

jshigetomi closed this Jan 13, 2026

github-project-automation Bot moved this from PR In Progress to Done in PowerShell Team Reviews/Investigations Jan 13, 2026

jshigetomi reopened this Jan 13, 2026

Make tests platform aware

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Copilot AI review requested due to automatic review settings January 13, 2026 19:02

Copilot started reviewing on behalf of jshigetomi January 13, 2026 19:02 View session

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Comment thread test/powershell/Modules/Microsoft.PowerShell.Utility/ConvertFrom-Csv.Tests.ps1 Outdated

jshigetomi and others added 2 commits January 13, 2026 13:25

Update test/powershell/Modules/Microsoft.PowerShell.Utility/ConvertFr…

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…om-Csv.Tests.ps1 Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Merge branch 'master' into fixNoValueCSVInput

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surfingoldelephant approved these changes Jan 21, 2026

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surfingoldelephant reviewed Jan 21, 2026

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Comment thread test/powershell/Modules/Microsoft.PowerShell.Utility/ConvertFrom-Csv.Tests.ps1

jshigetomi and others added 2 commits April 14, 2026 14:21

Merge branch 'master' into fixNoValueCSVInput

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