Fix NullReferenceException in tool install when package not found in manifest #52951

Copilot · 2026-02-10T19:00:05Z

Fix `dotnet tool install` NullReferenceException Regression

Summary

Fixes a critical regression in .NET 11.0.100-preview.2 where dotnet tool install would fail with "Unhandled exception: Object reference not set to an instance of an object."

Solution

Modified the shared ExplicitManifestOrFindManifestContainPackageId extension method to accept an optional throwIfNoManifestFound parameter:

For install: Pass false to allow manifest creation when none exists
For uninstall: Default true maintains existing behavior (throws if no manifest found)

This approach avoids code duplication and centralizes the manifest lookup logic in the shared method.

Changes

ToolManifestFinderExtensions.cs:
- Added throwIfNoManifestFound parameter (defaults to true)
- Removed #nullable disable and properly annotated nullable types
- Changed return type to (FilePath? filePath, string? warningMessage)
- Changed parameter to string? explicitManifestFile
ToolInstallLocalCommand.cs:
- Simplified to use shared method with throwIfNoManifestFound: false
- Updated to use string? for warningMessage
ToolUninstallLocalCommand.cs: No changes needed (uses default true behavior)
ToolInstallLocalCommandTests.cs: Added explicit regression test

Testing

✅ All 21 unit tests pass (20 existing + 1 new regression test)
✅ All 9 uninstall tests pass
✅ New test GivenExistingEmptyManifestItShouldInstallToolSuccessfully specifically covers the regression
✅ Manually verified exact repro scenario works
✅ Verified uninstall still throws when no manifest exists
✅ Proper nullability annotations prevent future NRT warnings

Risk Assessment

Low - Cleaner solution that leverages existing shared code with explicit regression coverage and proper nullability

Original prompt

This section details on the original issue you should resolve

<issue_title>[NETSDKE2E][Regression] With NET11.0 preview 2 SDK, 'dotnet tool' command fails - Unhandled exception: Object reference not set to an instance of an object.</issue_title>
<issue_description>REGRESSION INFO
Works well on 11.0.100-preview.1.26104.118

INSTALL STEPS

Install .NET 11.0.100-preview.2.26108.103 SDK on Windows11

REPRO STEPS

Create empty directory and cd to the directory

Run dotnet new tool-manifest

Run dotnet tool install dotnet-ef

EXPECTED
Run dotnet tool install dotnet-ef successfully.

ACTUAL
Shows Unhandled exception: Object reference not set to an instance of an object.

Dotnet --info
.NET SDK:
Version: 11.0.100-preview.2.26108.103
Commit: 8c56ff58fc
Workload version: 11.0.100-manifests.3e326a28
MSBuild version: 18.5.0-preview-26108-103+8c56ff58f

Runtime Environment:
OS Name: Windows
OS Version: 10.0.26200
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\11.0.100-preview.2.26108.103\

.NET workloads installed:
[wasm-tools]
Installation Source: SDK 11.0.100-preview.2
Manifest Version: 11.0.100-preview.2.26108.103/11.0.100-preview.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\11.0.100-preview.2\microsoft.net.workload.mono.toolchain.current\11.0.100-preview.2.26108.103\WorkloadManifest.json
Install Type: Msi

Configured to use workload sets when installing new manifests.
No workload sets are installed. Run "dotnet workload restore" to install a workload set.

Host:
Version: 11.0.0-preview.2.26108.103
Architecture: x64
Commit: 8c56ff58fc

.NET SDKs installed:
11.0.100-preview.2.26108.103 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 11.0.0-preview.2.26108.103 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 11.0.0-preview.2.26108.103 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 11.0.0-preview.2.26108.103 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
None

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download</issue_description>

<agent_instructions>Confirmed that this is broken in main but not in preview 1. Please take a look.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes [NETSDKE2E][Regression] With NET11.0 preview 2 SDK, 'dotnet tool' command fails - Unhandled exception: Object reference not set to an instance of an object. #52905

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

marcpopMSFT · 2026-02-11T00:47:22Z

@copilot I see that you modified ToolInstallLocalCommand. Wouldn't it be better to fix the shared method that is ExplicitManifestOrFindManifestContainPackageId to handle this situation rather than duplicating some of that code?

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Copilot · 2026-02-11T00:55:48Z

@copilot I see that you modified ToolInstallLocalCommand. Wouldn't it be better to fix the shared method that is ExplicitManifestOrFindManifestContainPackageId to handle this situation rather than dup...

You're absolutely right. I've refactored the fix to modify the shared ExplicitManifestOrFindManifestContainPackageId method instead of duplicating logic.

The method now accepts an optional throwIfNoManifestFound parameter (defaults to true for backward compatibility):

Install passes false to gracefully handle missing manifests
Uninstall uses the default true to maintain its existing behavior

Commit: 0c4ffbf

marcpopMSFT · 2026-02-12T18:41:40Z

Before

@marcpopMSFT ➜ /workspaces/test $ dotnet --version
11.0.100-preview.2.26111.109
@marcpopMSFT ➜ /workspaces/test $ dotnet tool install dotnetsay -g
Unhandled exception: Object reference not set to an instance of an object.

After

(dogfood) @marcpopMSFT ➜ /workspaces/test $ dotnet --version
11.0.100-dev
(dogfood) @marcpopMSFT ➜ /workspaces/test $ dotnet tool install dotnetsay -g
<snipped>
Tool 'dotnetsay' (version '3.0.3') was successfully installed.

marcpopMSFT · 2026-02-12T18:42:31Z

Same for local install.

baronfel · 2026-02-12T18:42:39Z

@copilot do we have any tests covering tool installation that should have detected this? If not, please create one so we don't regress this ability.

Copilot

Pull request overview

Fixes a regression in dotnet tool install where missing tool manifest discovery could surface as an unhandled exception, by allowing install to proceed and create/select a manifest when appropriate.

Changes:

Added an optional throwIfNoManifestFound parameter to ExplicitManifestOrFindManifestContainPackageId to optionally suppress manifest-not-found exceptions.
Updated local tool install to call the helper with throwIfNoManifestFound: false and fall back to GetManifestFilePath() when no manifest is found/selected.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Cli/dotnet/Commands/Tool/Install/ToolInstallLocalCommand.cs	Uses the updated helper with `throwIfNoManifestFound: false` and simplifies manifest selection/fallback logic.
src/Cli/dotnet/Commands/Tool/Common/ToolManifestFinderExtensions.cs	Adds optional behavior to suppress throwing when no manifest exists, enabling install to handle creation/fallback.

Copilot · 2026-02-12T18:52:35Z

src/Cli/dotnet/Commands/Tool/Common/ToolManifestFinderExtensions.cs

    public static (FilePath? filePath, string warningMessage) ExplicitManifestOrFindManifestContainPackageId(
        this IToolManifestFinder toolManifestFinder,
        string explicitManifestFile,
-        PackageId packageId)
+        PackageId packageId,
+        bool throwIfNoManifestFound = true)


warningMessage is declared as non-nullable (string) in the tuple return type, but this method returns null for it in several paths (explicit manifest, no match, and now the no-manifest catch). This makes the nullability contract incorrect for nullable-enabled callers and can lead to missed null checks / NRT warnings. Consider enabling nullable for this file (or at least for this method) and changing the signature to return string? warningMessage (and likewise accept string? explicitManifestFile).

@copilot apply changes based on this feedback

Fixed the nullability annotations:

Removed #nullable disable from ToolManifestFinderExtensions.cs

Changed return type to (FilePath? filePath, string? warningMessage)

Changed parameter to string? explicitManifestFile

Updated calling code in ToolInstallLocalCommand.cs to use string?

All tests pass (21 install + 9 uninstall).

Commit: 4921020

Copilot · 2026-02-12T18:52:35Z

src/Cli/dotnet/Commands/Tool/Install/ToolInstallLocalCommand.cs

        (FilePath? manifestFileOptional, string warningMessage) =
-            _toolManifestFinder.ExplicitManifestOrFindManifestContainPackageId(_explicitManifestFile, packageId);
+            _toolManifestFinder.ExplicitManifestOrFindManifestContainPackageId(_explicitManifestFile, packageId, throwIfNoManifestFound: false);

        if (warningMessage != null)
        {
            _reporter.WriteLine(warningMessage.Yellow());


In this nullable-enabled file, warningMessage is deconstructed as non-nullable string, but the called helper can return null for the warning. This forces a redundant warningMessage != null check (and can hide real nullability issues). After adjusting the helper’s signature, consider deconstructing into string? warningMessage here to match the actual behavior.

@copilot apply changes based on this feedback

This was already addressed in commit 4921020. Line 105 now uses string? warningMessage to properly match the nullable return type from the helper method.

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>

Copilot · 2026-02-12T18:53:33Z

@copilot do we have any tests covering tool installation that should have detected this? If not, please create one so we don't regress this ability.

Yes, we have existing unit tests that cover tool installation scenarios. The test ToolInstallLocalCommandTests.WhenRunWithPackageIdItShouldSaveToCacheAndAddToManifestFile tests installing into an existing empty manifest, which is the regression scenario.

However, I've added a more explicit regression test GivenExistingEmptyManifestItShouldInstallToolSuccessfully that specifically documents this case and includes a comment linking to the issue. All 21 unit tests now pass.

Commit: 14280f6

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Initial plan

1918794

Copilot AI assigned Copilot and marcpopMSFT Feb 10, 2026

Copilot started work on behalf of marcpopMSFT February 10, 2026 19:00 View session

Copilot AI and others added 2 commits February 10, 2026 19:20

Fix tool install NullReferenceException by reordering manifest lookup

c3841cb

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Address code review: improve warningMessage scoping

9d67e02

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix unhandled exception in dotnet tool command~~ Fix NullReferenceException in tool install when package not found in manifest Feb 10, 2026

Copilot AI requested a review from marcpopMSFT February 10, 2026 19:26

Copilot finished work on behalf of marcpopMSFT February 10, 2026 19:26

Copilot started work on behalf of marcpopMSFT February 11, 2026 00:47 View session

Refactor to fix issue in shared method instead of duplicating logic

0c4ffbf

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Copilot finished work on behalf of marcpopMSFT February 11, 2026 00:57

marcpopMSFT mentioned this pull request Feb 12, 2026

[dotnet-sdk-11.0.100-preview.2.26110.101] Execute commands "dotnet tool install -g XXX" or "dotnet tool install -global XXX" get error: Unhandled exception: Object reference not set to an instance of an object. #52976

Open

marcpopMSFT approved these changes Feb 12, 2026

View reviewed changes

marcpopMSFT requested a review from baronfel February 12, 2026 18:40

marcpopMSFT marked this pull request as ready for review February 12, 2026 18:42

Copilot AI review requested due to automatic review settings February 12, 2026 18:42

Copilot started reviewing on behalf of marcpopMSFT February 12, 2026 18:43 View session

Copilot started work on behalf of baronfel February 12, 2026 18:43 View session

Copilot AI reviewed Feb 12, 2026

View reviewed changes

Add regression test for installing into existing empty manifest

14280f6

Co-authored-by: baronfel <573979+baronfel@users.noreply.github.com>

Copilot finished work on behalf of baronfel February 12, 2026 18:54

Copilot started work on behalf of marcpopMSFT February 12, 2026 21:28 View session

Fix nullability annotations for warningMessage and explicitManifestFile

4921020

Co-authored-by: marcpopMSFT <12663534+marcpopMSFT@users.noreply.github.com>

Copilot AI requested a review from marcpopMSFT February 12, 2026 21:38

Copilot finished work on behalf of marcpopMSFT February 12, 2026 21:38

Copilot started work on behalf of marcpopMSFT February 12, 2026 21:38 View session

Copilot finished work on behalf of marcpopMSFT February 12, 2026 21:44

Fix NullReferenceException in tool install when package not found in manifest #52951

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Fix NullReferenceException in tool install when package not found in manifest #52951

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Fix dotnet tool install NullReferenceException Regression

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Fix `dotnet tool install` NullReferenceException Regression