[release/10.0] Fix NullReferenceException in dbcontext optimize with cross-version compatibility

[Copilot]

Fixes #36437

Description

The dotnet ef dbcontext optimize command throws a NullReferenceException when using dotnet-ef tools version 9.0 or later with EF Core 8.0 projects, despite successfully generating the compiled model.

Customer impact

When customers use dotnet-ef tools 9.0+ with EF Core 8.0 projects and run dotnet ef dbcontext optimize, they see a NullReferenceException error message after the compiled model is successfully generated. The error appears at DbContextOptimizeCommand.ReportResults(IEnumerable<string> generatedFiles) when attempting to iterate over a null result.

While the compiled model files are still created correctly, the error message can be confusing and may cause build pipeline failures if not handled properly.

Workaround: Customers can either:

1. Use dotnet-ef tools 8.0.22 or earlier with EF Core 8.0 projects, or
2. Upgrade to EF Core 9.0+ to match their dotnet-ef tools version

How found

Multiple customer reports on EF 9.0.x and 10.0.x

Regression

Yes, introduced in #33028 (part of #24894). The issue occurs because:

Testing

Verified manually

Risk

Low. The change is minimal (3-line addition).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>NullReferenceException when running dotnet ef dbcontext optimize</issue_title>
<issue_description>### Bug description

Hi,
Whenever I run the optimize command on a scaffolded model I get the error:
dotnet ef dbcontext optimize -o Models --no-build
Successfully generated a compiled model, to use it call 'options.UseModel(NBWebSeed1ContextModel.Instance)'. Run this command again when the model is modified.
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.EntityFrameworkCore.Tools.Commands.DbContextOptimizeCommand.ReportResults(IEnumerable`1 generatedFiles)
at Microsoft.EntityFrameworkCore.Tools.Commands.DbContextOptimizeCommand.Execute(String[] args)
at Microsoft.EntityFrameworkCore.Tools.Commands.CommandBase.<>c__DisplayClass0_0.b__0(String[] args)
at Microsoft.DotNet.Cli.CommandLine.CommandLineApplication.Execute(String[] args)
at Microsoft.EntityFrameworkCore.Tools.Program.Main(String[] args)
Object reference not set to an instance of an object.

Your code

dotnet ef dbcontext optimize -o Models --no-build
My tool version is 9.0.7 but I'm running the command against a model that targets .NET 8 and depends on Microsoft.EntityFrameworkCore.SqlServer 8.0.15

Stack traces

Verbose output

EF Core version

9.0.7

Database provider

Microsoft.EntityFrameworkCore.SqlServer

Target framework

.NET 8.0

Operating system

Windows 10

IDE

Visual Studio 17.4.9</issue_description>

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

@AndriySvyryd Could you share a small standalone repro project? @AndriySvyryd Related to #35219

• Fixes NullReferenceException when running dotnet ef dbcontext optimize #36437

---

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

[AndriySvyryd]

@copilot Update progress by rewriting the PR summary using this template:

Fixes #{number}

**Description**
{Issue description}

**Customer impact**
{How does the reported issue affects customer's app? Are there workarounds?}

**How found**
{Was it customer reported or found during verification? How many customers are affected?}

**Regression**
{Is it a regression from a released version? Which one?}

**Testing**
{How the changes were tested}

**Risk**
{Low/Medium/High, argument why}

[Copilot]

@copilot Update progress by rewriting the PR summary using this template:

...

Updated the PR description with the structured template.

[Copilot]

Pull request overview

This PR fixes a NullReferenceException in the dotnet ef dbcontext optimize command when using dotnet-ef tools version 9.0+ with EF Core 8.0 projects. The issue occurs because DbContextOperations.Optimize changed its return type from void (8.0) to IReadOnlyList<string> (9.0+), causing the tools to receive a null result when operating on EF Core 8.0 projects. The fix adds a null check before attempting to report results.

Changes:

• Added null check before calling ReportResults in DbContextOptimizeCommand.Execute to handle cross-version compatibility

[artl93]

Regression, customer reported, non-obvious workaround, approved.