NullableIssue.cs

class C1
{
	[Test]
	public void METHOD()
	{
		var lookupValue1 = Lookup(new Dictionary<string, string?>(), "a");
		var lookupValue2 = Lookup(new Dictionary<string, string>(), "a");
	}

	public LookupValue<TV> Lookup<TK, TV>(Dictionary<TK, TV?> d, TK key) 
		where TK : notnull
		where TV : notnull
	{
		if (d.TryGetValue(key, out var result))
		{
			return new LookupValue<TV>(result);
		}
		else
		{
			return new LookupValue<TV>(default);
		}
	}

	public record LookupValue<T>(T? Value) where T : notnull;
}