Object reference not set to an instance of an object. MVC and Foreign Key

I tried everything and nothing! It’s returning the following message: "System.NullReferenceException: ‘Object reference not set to an instance of an object.’"

Maybe it’s because I use two foreign keys of the same class!? I don’t know… Give me a light, please lol.

 public List<atendimento> ListarAtendimentos()
    {
        List<atendimento> lst = new List<atendimento>();

        using (SqlConnection con = new SqlConnection(cs))
        {
            con.Open();
            SqlCommand com = new SqlCommand("SELECT *, c.nome as nome_cartorio, a.status as status_atendimento, u.nome as nome_usuario FROM atendimento AS a INNER JOIN usuarios AS u ON u.id = a.id_usuario_cadastro INNER JOIN cartorios AS c ON a.id_cartorio = c.id", con);
            SqlDataReader rdr = com.ExecuteReader();
            while (rdr.Read())
            {
                atendimento ate = new atendimento();
                ate.cartorios = new cartorios();

                ate.id = Convert.ToInt32(rdr["id"]);
                ate.id_cartorio = Convert.ToInt32(rdr["id_cartorio"]);
                ate.cartorios.nome = rdr["nome_cartorio"].ToString();
                ate.titulo = rdr["titulo"].ToString();
                ate.descricao = rdr["descricao"].ToString();
                ate.data_abertura = Convert.ToDateTime(rdr["data_abertura"]);
                if (!rdr.IsDBNull(rdr.GetOrdinal("data_conclusao")))
                {
                    ate.data_conclusao = Convert.ToDateTime(rdr["data_conclusao"]);
                }
                ate.contato = rdr["contato"].ToString();
                ate.origem = rdr["origem"].ToString();
                ate.prioridade = rdr["prioridade"].ToString();
                ate.status = rdr["status_atendimento"].ToString();
                ate.usuarios.nome = rdr["nome_usuario"].ToString();
                ate.id_usuario_cadastro = Convert.ToInt32(rdr["id_usuario_cadastro"]);
                ate.id_usuario_atendimento = Convert.ToInt32(rdr["id_usuario_atendimento"]);

                lst.Add(ate);
            }
            return lst;
        }
    }

The problem is in the following line:

ate.usuarios.nome = rdr["nome_usuario"].ToString();

Class 1:

public partial class atendimento
    {
        public atendimento()
        {
            this.lancamentos = new HashSet<lancamentos>();
        }

        public int id { get; set; }
        public int id_cartorio { get; set; }
        public string titulo { get; set; }
        public string descricao { get; set; }
        public Nullable<System.DateTime> data_abertura { get; set; }
        public Nullable<System.DateTime> data_conclusao { get; set; }
        public string contato { get; set; }
        public string origem { get; set; }
        public string prioridade { get; set; }
        public string status { get; set; }
        public int id_usuario_cadastro { get; set; }
        public int id_usuario_atendimento { get; set; }
        public virtual usuarios usuarios { get; set; }
        public virtual cartorios cartorios { get; set; }
        public virtual usuarios usuarios1 { get; set; }
        public virtual ICollection<lancamentos> lancamentos { get; set; }
    }

Class 2:

public partial class usuarios
    {
        public usuarios()
        {
            this.anexos = new HashSet<anexos>();
            this.atendimento = new HashSet<atendimento>();
            this.atendimento1 = new HashSet<atendimento>();
            this.lancamentos = new HashSet<lancamentos>();
            this.lancamentos1 = new HashSet<lancamentos>();
        }

        public int id { get; set; }
        public string nome { get; set; }
        public string email { get; set; }
        public string senha { get; set; }
        public string status { get; set; }
        public string acesso { get; set; }
        public int id_setor { get; set; }

        public virtual ICollection<anexos> anexos { get; set; }
        public virtual ICollection<atendimento> atendimento { get; set; }
        public virtual ICollection<atendimento> atendimento1 { get; set; }
        public virtual ICollection<lancamentos> lancamentos { get; set; }
        public virtual ICollection<lancamentos> lancamentos1 { get; set; }
        public virtual setor setor { get; set; }
    }

>Solution :

usuarios is not created , try this

 while (rdr.Read())
{
var ate = new atendimento{
cartorios = new cartorios(),
usuarios=new usuarious()
}
....