System.CodeDom.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppPrevious);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>

    <!-- TODO https://github.com/dotnet/runtime/issues/90400: Annotate for nullable reference types -->
    <Nullable>disable</Nullable>
    <NoWarn>$(NoWarn);nullable</NoWarn>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="System.CodeDom.cs" Condition="'$(TargetFrameworkIdentifier)' != '.NETFramework'" />
    <Compile Include="System.CodeDom.netframework.cs" Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'" />
  </ItemGroup>
</Project>