Nullable warning within nested LINQ

[MarvinKlein1508]

Describe the bug

I want to select an array from a property from a nullable reference. In my where clause I specify that my object cannot be null, however within my .Select I get a CS8602 Dereference of a possibly null reference warning.
Bestellungen.Where(x => x.Lieferant is not null).Select(x => x.Lieferant.LieferantId).ToArray();

I guess the compiler should be able to detect that I allready checked against null at this point. However I simply added an ! there but I think this might be confusing at some point.

Further technical details

• ASP.NET Core version 5.0.0-rc.1.20451.14
• C# 9.0
  .NET Core SDK (gemäß "global.json"):
  Version: 5.0.100-rc.1.20452.10
  Commit: 473d1b592e

Laufzeitumgebung:
OS Name: Windows
OS Version: 10.0.19041
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\5.0.100-rc.1.20452.10\

Host (useful for support):
Version: 5.0.0-rc.1.20451.14
Commit: 38017c3

.NET SDKs installed:
3.1.400-preview-015203 [C:\Program Files\dotnet\sdk]
3.1.402 [C:\Program Files\dotnet\sdk]
5.0.100-rc.1.20452.10 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.0-rc.1.20451.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.22 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.0-rc.1.20451.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.0-rc.1.20452.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET runtimes or SDKs:
https://aka.ms/dotnet-download

• The IDE VS Version 16.8.0 Preview 3.2

[ghost]

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[huoyaoyuan]

This is expected.

I guess the compiler should be able to detect that I allready checked against null at this point.

The compiler has no knowledge of Where and its behavior.

See dotnet/csharplang#3951 .

[stephentoub]

Closing as dup of dotnet/csharplang#3951