[Serializable]
    public abstract class Entity<T> : IEquatable<T>
    {
          protected Entity()
        {
            Id = long.MinValue;
            Key = Guid.NewGuid();
            Visibility = Visibilities.Visible;
            DateCreation = new DateTime();
        }

        public long Id { get; set; }

         public Guid Key { get; set; }

        public bool IsNew => (Id == long.MinValue);

        public Visibilities Visibility { get; set; }
        
        public DateTime DateCreation { get; set; }

        public DateTime DateModification { get; set; }

        public int CreatorId { get; set; }

        public int ModifierId { get; set; }

        public bool Equals(Entity<T> other)
        {
            if (other is null)
            {
                return false;
            }

            if (ReferenceEquals(this, other))
            {
                return true;
            }

            if (this.GetType() != other.GetType())
            {
                return false;
            }

            bool otherIsTransient = Equals(other.Key, Guid.Empty);
            bool thisIsTransient = Equals(Key, Guid.Empty);

            if (otherIsTransient && thisIsTransient)
            {
                return ReferenceEquals(other, this);
            }

            return other.Key.Equals(Key);
        }

        public override bool Equals(object other) => other is Entity<T> entity && Equals(entity);

        public bool Equals([AllowNull] T other)
        {
            if (other == null)
            {
                return false;
            }

            return this.Equals(other);
        }

        public static bool operator ==(Entity<T> a, Entity<T> b)
        {
            if (a is null && b is null)
            {
                return true;
            }

            if (a is null || b is null)
            {
                return false;
            }

            return a.Equals(b);
        }

        public static bool operator !=(Entity<T> a, Entity<T> b)
        {
            return !(a == b);
        }

        public override int GetHashCode() => (Id, Key).GetHashCode();
    }

    [Serializable]
    public sealed class Participant : Entity<Participant>
    {

        public string Email { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }
    }

{"Object reference not set to an instance of an object."}
at RepoDb.Extensions.PropertyInfoExtension.GetHandledValue(PropertyInfo property, Object entity, Type declaringType)
   at RepoDb.Extensions.PropertyInfoExtension.GetHandledValue(PropertyInfo property, Object entity)
   at RepoDb.Extensions.PropertyInfoExtension.AsQueryField(PropertyInfo property, Object entity, Boolean appendUnderscore)
   at RepoDb.Extensions.PropertyInfoExtension.AsQueryField(PropertyInfo property, Object entity)
   at RepoDb.DbConnectionExtension.ToQueryGroup[TEntity](ClassProperty property, TEntity entity)
   at RepoDb.DbConnectionExtension.Update[TEntity](IDbConnection connection, TEntity entity, String hints, Nullable`1 commandTimeout, IDbTransaction transaction, ITrace trace, IStatementBuilder statementBuilder)
   at repository.Save(Participant participant) in **********\Repository.cs:line 35