In Memory DATABase troubles

    public class InMemoryDatabase
    {
        public Dictionary<int, Person> People = [];
        public Dictionary<int, List<int>>? Friends { get; set; } = [];


        public void AddPerson(int id, string? name, int? age) => 
            People.Add(id, new Person(id, name, age));

        public string? FetchPerson(int personId) =>
            People.TryGetValue(personId, out var foundPerson) ? foundPerson.ToString() : null;

        public void UpdatePerson(int personId, Person updatedPerson) 
        {
            if (People.TryGetValue(personId, out var foundPerson))
                People[foundPerson.Id] = updatedPerson;
        }
        public void RemovePerson(int personId)
        {
            if (People.TryGetValue(personId, out var foundPerson))
                People.Remove(foundPerson.Id);
        }
        public IEnumerable<string>? GetFriends(int personId)
        {
            if(Friends == null)
                throw new Exception("No Friends list available");
            if (Friends.TryGetValue(personId, out var friendIds))
                return People.Where(x => friendIds.Contains(x.Key)).Select(x => x.ToString());
            else
                return null;
        }
    }