Nullable dereference in collection expressions not raising any warning at build time

[cfbao]

Describe the bug

"CS8602 - Dereference of a possibly null reference" isn't raised at build time (with dotnet build) when the error is in a collection expression.

To Reproduce

List<string>? a = null;
string[]? c = [.. a];

In VS Code (with C# extension) I can see a yellow squiggly line under a at line 2, but when running dotnet build, there's no warning raised.

When <WarningsAsErrors>nullable</WarningsAsErrors> is set on the project, the build should fail, but doesn't.

Further technical details

dotnet --info output:

.NET SDK:
 Version:           8.0.404
 Commit:            7b190310f2
 Workload version:  8.0.400-manifests.b1234fe1
 MSBuild version:   17.11.9+a69bbaaf5

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19045
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.404\

.NET workloads installed:
Configured to use loose manifests when installing new manifests.
There are no installed workloads to display.

Host:
  Version:      9.0.0
  Architecture: x64
  Commit:       9d5a6a9aa4

.NET SDKs installed:
  8.0.404 [C:\Program Files\dotnet\sdk]
  9.0.101 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 8.0.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  C:\Users\cbao\Downloads\cstest\hello\global.json

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

Download .NET:
  https://aka.ms/dotnet/download

IDE: VS Code with C# extension (no C# Dev Kit)