Object reference not set to an instance

"Object reference not set to an instance" of an object I'm having this problem here in my project in ASP.NET and since for quite some time I can not get on with it, please can I take a look at my code and identify the error I need to help with it in the insert part part of the database I've already checked and it's not the problem I imagine it has to do with instantiating a new object but I can not identify it.

  //Acesso ao banco de dados
 public class BDAcesso
{
    private static SqlConnection _connection()
    {
        return new SqlConnection(Settings.Default.stringConexao);
    }

    private readonly SqlParameterCollection _sqlParameterCollection = new SqlCommand().Parameters;

    public void LimparParamentros()
    {
        _sqlParameterCollection.Clear();
    }

    public void AdicionarParamentros(string nomeParametro, object valorParametro)
    {
        _sqlParameterCollection.Add(new SqlParameter(nomeParametro, valorParametro));
    }

    public object ExecutarManipulacao(CommandType commandType, string stroredProcedure)
    {
        try
        {
            var sqlConnection = _connection();
            sqlConnection.Open();
            var sqlCommand = sqlConnection.CreateCommand();
            sqlCommand.CommandType = commandType;
            sqlCommand.CommandText = stroredProcedure;
            sqlCommand.CommandTimeout = 60;
            foreach (SqlParameter sqlParameter in _sqlParameterCollection)
            {
                sqlCommand.Parameters.Add(new SqlParameter(sqlParameter.ParameterName, sqlParameter.Value));
            }
            return sqlCommand.ExecuteScalar();
        }
        catch (Exception exception)
        {

            throw new Exception(exception.Message);
        }

    }

    public DataTable ExecutarConsulta(CommandType commandType, string stroredProcedure)
    {
        try
        {
            var sqlConnection = _connection();
            sqlConnection.Open();
            var sqlCommand = sqlConnection.CreateCommand();
            sqlCommand.CommandType = commandType;
            sqlCommand.CommandText = stroredProcedure;
            sqlCommand.CommandTimeout = 60;
            foreach (SqlParameter sqlParameter in _sqlParameterCollection)
            {
                sqlCommand.Parameters.Add(new SqlParameter(sqlParameter.ParameterName, sqlParameter.Value));
            }

            var sqlDataAdapter = new SqlDataAdapter(sqlCommand);
            var dataTable = new DataTable();
            sqlDataAdapter.Fill(dataTable);
            return dataTable;

        }
        catch (Exception exception)
        {

            throw new Exception(exception.Message);
        }

    }
}

 //DAO------------------------------------------------

 public string InserirCliente(Clientes clientes)
    {
        try
        {
            _bdAcesso.LimparParamentros();

            _bdAcesso.AdicionarParamentros("@Nome", clientes.Nome);
            _bdAcesso.AdicionarParamentros("@NomeFantasia", clientes.NomeFantasia);
            _bdAcesso.AdicionarParamentros("@CPF_CNPJ", clientes.CPF_CNPJ);
            _bdAcesso.AdicionarParamentros("@RG_IE", clientes.RG_IE);
            _bdAcesso.AdicionarParamentros("@Obs", clientes.Obs);
            _bdAcesso.AdicionarParamentros("@Responsavel", clientes.Responsavel);
            _bdAcesso.AdicionarParamentros("@Logradouro", clientes.Endereco.Logradouro);
            _bdAcesso.AdicionarParamentros("@Bairro", clientes.Endereco.Bairro);
            _bdAcesso.AdicionarParamentros("@Cidade", clientes.Endereco.Cidade);
            _bdAcesso.AdicionarParamentros("@Estado", clientes.Endereco.Estado);
            _bdAcesso.AdicionarParamentros("@Uf", clientes.Endereco.Uf);
            _bdAcesso.AdicionarParamentros("@Cep", clientes.Endereco.Cep);
            _bdAcesso.AdicionarParamentros("@Complemento", clientes.Endereco.Complemento);
            _bdAcesso.AdicionarParamentros("@Fixo", clientes.Contato.Fixo);
            _bdAcesso.AdicionarParamentros("@Celular", clientes.Contato.Celular);
            _bdAcesso.AdicionarParamentros("@Comercial", clientes.Contato.Comercial);
            _bdAcesso.AdicionarParamentros("@Email", clientes.Contato.Email);
            _bdAcesso.AdicionarParamentros("@HomePage", clientes.Contato.HomePage);

            var idCliente = _bdAcesso.ExecutarManipulacao(CommandType.StoredProcedure, "uspInserirCliente").ToString();
            return idCliente;
        }
        catch (Exception exception)
        {

            throw new Exception(exception.Message);
        }

    }

//Controle
    [HttpPost]
    public ActionResult Create(FormCollection collection)
    {
        try
        {
        var clienteDao = new ClienteDao();

        var cliente = new Clientes
        {
            Nome = collection["Nome"],
            NomeFantasia = collection["NomeFantasia"],
            CPF_CNPJ = collection["CPF_CNPJ"],
            RG_IE = collection["RG_IE"],
            Obs = collection["Obs"],
            AlteradoPor = collection["AlteradoPor"],
            Responsavel = collection["Responsavel"],
            Contato =
            new Contato
            {
                Fixo = collection["Fixo"],
                Celular = collection["Celular"],
                Comercial = collection["Comercial"],
                Email = collection["Email"],
                HomePage = collection["HomePage"]
            },
            Endereco =
            new Endereco
            {
                Logradouro = collection["Logradouro"],
                Bairro = collection["Bairro"],
                Cidade = collection["Cidade"],
                Estado = collection["Estado"],
                Uf = collection["Uf"],
                Cep = collection["Cep"],
                Complemento = collection["Complemento"]
            }
        };


        clienteDao.InserirCliente(cliente);
        return RedirectToAction("Index");
        }
        catch
        {
            return View();
        }
    }

This is the error after you remove all try :

Procedure or function 'uspInserirCliente' expects parameter '@Fixo', which was not supplied.