Unity Object reference not set to an instance of an object

I'm doing a Quiz on Unity and I'm having an error that I can not solve, I already looked for similar errors but I can not identify, this message appears when I'm running the quiz

  

NullReferenceException: Object reference not set to an instance of an   object GameController.Start () (at Assets / GameController.cs: 39)

This is the GameController

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

public class GameController : MonoBehaviour {

public Text textoPergunta;
public Text textoPontos;
public Text textoTimer;
public Text highScoreText;

public SimpleObjectPool answerButtonObjectPool;
public Transform answerButtonParent;
public GameObject painelDePerguntas;
public GameObject painelFimRodada;

private DataController dataController;
public RoundData rodadaAtual;
private QuestionData[] questionPool;

private bool rodadaAtiva;
private float tempoRestante;
private int questionIndex;
private int playerScore;

List<int> usedValues = new List<int>();

private List<GameObject> answerButtonGameObjects = new List<GameObject>();



// Use this for initialization
void Start () {


    dataController = FindObjectOfType<DataController>();


    rodadaAtual = dataController.GetCurrentRoundData();                   //ERRO Some quando tiro essas linhas      
    questionPool = rodadaAtual.perguntas;                                 //ERRO   
    tempoRestante = rodadaAtual.limiteDeTempo;                            //ERRO

    UpdateTimer();

    playerScore = 0;
    questionIndex = 0;
    ShowQuestion();
    rodadaAtiva = true;

}

// Update is called once per frame
void Update () {

    if (rodadaAtiva)
    {
        tempoRestante -= Time.deltaTime;
        UpdateTimer();

        if (tempoRestante <= 0)
        {
            endRound();
        }
    }


}


// Funções
private void UpdateTimer()
{
    textoTimer.text = "Timer: " + Mathf.Round(tempoRestante).ToString();
}


private void ShowQuestion()
{
    RemoveAnswerButtons();

    int random = Random.Range(0, questionPool.Length);
    while (usedValues.Contains(random))
    {
        random = Random.Range(0, questionPool.Length);
    }
    QuestionData questionData = questionPool[random];
    usedValues.Add(random);
    textoPergunta.text = questionData.textoDaPergunta;


    for (int i = 0; i < questionData.respostas.Length; i++)
    {
        GameObject answerButtonGameObject = answerButtonObjectPool.GetObject();

        answerButtonGameObject.transform.SetParent(answerButtonParent);

        answerButtonGameObjects.Add(answerButtonGameObject);

        AnswerButton answerButton = answerButtonGameObject.GetComponent<AnswerButton>();
        answerButton.Setup(questionData.respostas[i]);
    }
}

private void RemoveAnswerButtons()
{
    while(answerButtonGameObjects.Count > 0)
    {
        answerButtonObjectPool.ReturnObject(answerButtonGameObjects[0]);
        answerButtonGameObjects.RemoveAt(0);
    }
}

public void AnswerButtonClicked(bool estaCorreto)
{
    if (estaCorreto)
    {
        playerScore += rodadaAtual.pontosPorAcerto;
        textoPontos.text = "Score: " + playerScore.ToString();
    }

    if(questionPool.Length > questionIndex + 1)
    {
        questionIndex++;
        ShowQuestion();
    }
    else
    {
        endRound();
    }

}
    public void endRound()
    {
        rodadaAtiva = false;

    painelDePerguntas.SetActive(false);
    painelFimRodada.SetActive(true);
    }

public void ReturnToMenu()
{
    SceneManager.LoadScene("Menu");
}

}

I've noticed that every time I% s and datacontroller.getcurrentRoundData it with this error, but I can not see where the error is in that function or in subsequent ones, since this GetCurrentRoundData looks like this:

public RoundData GetCurrentRoundData()
{
    return todasAsRodadas[rodadaIndex];
}

I do not know if the error is really there and I can not identify, what I checked was that taking the rows of the current Current it to give this error, now how to solve I do not know, if you are saying something the codes are zipped in the link below the dropbox, I'm following a tutorial but the code is apparently identical to the one in the tutorial: link of the tutorial

link to files in DropBox