<PackageReference Include="NUnit" Version="4.2.2" />

NullConstraint

public class NullConstraint : Constraint
NullConstraint tests that the actual value is null
using System; using System.Runtime.CompilerServices; namespace NUnit.Framework.Constraints { [System.Runtime.CompilerServices.NullableContext(1)] [System.Runtime.CompilerServices.Nullable(0)] public class NullConstraint : Constraint { public override string Description => "null"; public override ConstraintResult ApplyTo<[System.Runtime.CompilerServices.Nullable(2)] TActual>(TActual actual) { return new ConstraintResult(this, actual, actual == null); } public NullConstraint() : base(Array.Empty<object>()) { } } }