<PackageReference Include="System.Text.Encodings.Web" Version="6.0.0-preview.2.21154.6" />

MemberNotNullWhenAttribute

namespace System.Diagnostics.CodeAnalysis { [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)] internal sealed class MemberNotNullWhenAttribute : Attribute { public bool ReturnValue { get; } public string[] Members { get; } public MemberNotNullWhenAttribute(bool returnValue, string member) { ReturnValue = returnValue; Members = new string[1] { member }; } public MemberNotNullWhenAttribute(bool returnValue, params string[] members) { ReturnValue = returnValue; Members = members; } } }