Date value coming 01/01/0001.00:00:00

Question

I’m having a problem with my API when I try to rescue a date from a column in my table in Sqlserver

I’m doing it this way

using (SqlCommand command = new SqlCommand()) {
                        command.Connection = connection;
                        command.CommandText = "SELECT TOP 1 DateStart, DateEnd from CheckUP where DeviceIMEI = @imei ORDER BY DateStart DESC";
                        command.Parameters.AddWithValue("imei", obj.DeviceIMEI);
                        SqlDataReader reader = command.ExecuteReader();

                        while (reader.Read()) {
                            CheckUP check = new CheckUP() {
                                DateStart = reader["DateStart"] == DBNull.Value ? DateTime.MinValue : Convert.ToDateTime(reader["DateStart"]),
                                DateEnd = reader["DateEnd"] == DBNull.Value ? DateTime.MinValue : Convert.ToDateTime(reader["DateEnd"]),
                            };

                            if (reader.IsDBNull(1) == true) {
                                System.DateTime today = DateTime.Today;

                                Debug.WriteLine("hoje"+ today);
                                Debug.WriteLine("data do banco" +  checkup.DateStart);

                                TimeSpan diferenceToday = today - checkup.DateStart;
                                totalLifeCheckUpProgress = diferenceToday.ToString();
                                Debug.WriteLine("Resultado"+totalLifeCheckUpProgress);
                            } else {
                                TimeSpan difetenceEnd = checkup.DateStart - checkup.DateEnd;
                                totalLifeCheckUpProgress = difetenceEnd.ToString();
                                Debug.WriteLine(totalLifeCheckUpProgress);
                            }
                        }
                    }

From what I understand this value being returned 01/01/0001.00:00:00 should be returned only if the value is null or less than 01/01/1970

but the value of the camnpo where I am rescuing is not null nor me nor nor me nor what 01/01/1970

the data type in the database is as smalldateTime

what I can is wrong ?