<PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="11.0.0-preview.1.26104.118" />

System.Diagnostics.CodeAnalysis.MaybeNullAttribute

sealed class MaybeNullAttribute : Attribute
Specifies that an output may be null even if the corresponding type disallows it.
namespace System.Diagnostics.CodeAnalysis { internal sealed class MaybeNullAttribute : Attribute { public MaybeNullAttribute(); } }