Fix NullReferenceException in dbcontext optimize with cross-version compatibility

[Copilot]

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

Root Cause

EF Core 8.0's DbContextOperations.Optimize returns void, while 9.0+ returns IReadOnlyList<string>. When the 9.0+ tool invokes the 8.0 runtime via reflection, it receives null and attempts to enumerate it in ReportResults.

Changes

• Add null check before calling ReportResults in DbContextOptimizeCommand.Execute
• Preserves file path reporting for 9.0+ while maintaining backward compatibility with 8.0

var result = executor.OptimizeContext(...);

if (result != null)
{
    ReportResults(result);
}

This aligns with the tool's cross-version support pattern established in #37201.

Original prompt

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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

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