<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.4" />

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(); } }