Proposal aggregate pseudo code showing its integrity with comments

Proposal.cs

public class Proposal
{
    private List<Comments> _comments;
    public IReadOnlyList<Comments> Comments => _comments.AsReadOnly();
    private bool IsOpenForDiscussion => Status != ProposalStatus.Pending;

    public void Discuss(Guid userId, string content)
    {
        if(!IsOpenForDiscussion)
            throw new DomainException("Can't discuss about an closed proposal");

        _comments.Add(new Comment(userId, Id, content));
    }
}