I am getting a fatal exception when I execute my code. Can someone please help me out

public static final String TAG = MainActivity.class.getSimpleName();

private Forecast mForecast;

@InjectView(R.id.timeLabel) TextView mTimeLabel;
@InjectView(R.id.temperatureLabel) TextView mTemperatureLabel;
@InjectView(R.id.humidityValue) TextView mHumidityValue;
@InjectView(R.id.precipValue) TextView mPrecipValue;
@InjectView(R.id.summaryLabel) TextView mSummaryLabel;
@InjectView(R.id.iconImageView) ImageView mIconImageView;
@InjectView(R.id.refreshImageView) ImageView mRefreshImageView;
@InjectView(R.id.progressBar) ProgressBar mProgressBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.inject(this);

    mProgressBar.setVisibility(View.INVISIBLE);

    final double latitude = 37.8267;
    final double longitude = -122.423;

    mRefreshImageView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            getForecast(latitude, longitude);
        }
    });

    getForecast(latitude, longitude);

    Log.d(TAG, "Main UI code is running!");
}

private void getForecast(double latitude, double longitude) {
    String apiKey = "27974c4bc33201748eaf542a6769c3b7";
    String forecastUrl = "https://api.forecast.io/forecast/" + apiKey +
            "/" + latitude + "," + longitude;

    if (isNetworkAvailable()) {
        toggleRefresh();

        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(forecastUrl)
                .build();

        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Request request, IOException e) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        toggleRefresh();
                    }
                });
                alertUserAboutError();
            }

            @Override
            public void onResponse(Response response) throws IOException {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        toggleRefresh();
                    }
                });

                try {
                    String jsonData = response.body().string();
                    Log.v(TAG, jsonData);
                    if (response.isSuccessful()) {
                        mForecast = parseForecastDetails(jsonData);
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                updateDisplay();
                            }
                        });
                    } else {
                        alertUserAboutError();
                    }
                }
                catch (IOException e) {
                    Log.e(TAG, "Exception caught: ", e);
                }
                catch (JSONException e) {
                    Log.e(TAG, "Exception caught: ", e);
                }
            }
        });
    }
    else {
        Toast.makeText(this, getString(R.string.network_unavailable_message),
                Toast.LENGTH_LONG).show();
    }
}

private void toggleRefresh() {
    if (mProgressBar.getVisibility() == View.INVISIBLE) {
        mProgressBar.setVisibility(View.VISIBLE);
        mRefreshImageView.setVisibility(View.INVISIBLE);
    }
    else {
        mProgressBar.setVisibility(View.INVISIBLE);
        mRefreshImageView.setVisibility(View.VISIBLE);
    }
}

private void updateDisplay() {
    Current mCurrent = mForecast.getCurrent();
    mTemperatureLabel.setText(mCurrent.getTemperature() + "");
    mTimeLabel.setText("At " + mCurrent.getFormattedTime() + " it will be");
    mHumidityValue.setText(mCurrent.getHumidity() + "");
    mPrecipValue.setText(mCurrent.getPrecipChance() + "%");
    mSummaryLabel.setText(mCurrent.getSummary());

    Drawable drawable = getResources().getDrawable(mCurrent.getIconId());
    mIconImageView.setImageDrawable(drawable);
}

private Current getCurrentDetails(String jsonData) throws JSONException {
    JSONObject forecast = new JSONObject(jsonData);
    String timezone = forecast.getString("timezone");
    Log.i(TAG, "From JSON: " + timezone);

    JSONObject currently = forecast.getJSONObject("currently");

    Current current = new Current();
    current.setHumidity(currently.getDouble("humidity"));
    current.setTime(currently.getLong("time"));
    current.setIcon(currently.getString("icon"));
    current.setPrecipChance(currently.getDouble("precipProbability"));
    current.setSummary(currently.getString("summary"));
    current.setTemperature(currently.getDouble("temperature"));
    current.setTimeZone(timezone);

    Log.d(TAG, current.getFormattedTime());

    return current;
}


private boolean isNetworkAvailable() {
    ConnectivityManager manager = (ConnectivityManager)
            getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = manager.getActiveNetworkInfo();
    boolean isAvailable = false;
    if (networkInfo != null && networkInfo.isConnected()) {
        isAvailable = true;
    }

    return isAvailable;
}

private void alertUserAboutError() {
    AlertDialogFragment dialog = new AlertDialogFragment();
    dialog.show(getFragmentManager(), "error_dialog");
}

private Forecast parseForecastDetails(String jsonData) throws JSONException {
    Forecast forecast = new Forecast();
    forecast.setCurrent(getCurrentDetails(jsonData));
    forecast.setHourlyForecast(getHourlyForecast(jsonData));
    forecast.setDailyForecast(getDailyForecast(jsonData));
    return forecast;
}

private Hour[] getHourlyForecast(String jsonData) throws JSONException {
    JSONObject forecast = new JSONObject(jsonData);
    String timezone = forecast.getString("timezone");
    JSONObject hourly = forecast.getJSONObject("hourly");
    JSONArray data = hourly.getJSONArray("data");

    Hour hours[] = new Hour[data.length()];

    for(int i=0;i<data.length();i++) {
        JSONObject jsonHour = data.getJSONObject(i);
        hours[i].setSummary(jsonHour.getString("summary"));
        hours[i].setTimeZone(timezone);
        hours[i].setTime(jsonHour.getLong("time"));
        hours[i].setTemperature(jsonHour.getDouble("temperature"));
        hours[i].setIcon(jsonHour.getString("icon"));
    }

    return hours;
}

private Day[] getDailyForecast(String jsonData) throws JSONException {
    JSONObject forecast = new JSONObject(jsonData);
    String timezone = forecast.getString("timezone");
    JSONObject daily = forecast.getJSONObject("daily");
    JSONArray data = daily.getJSONArray("data");

    Day days[] = new Day[data.length()];

    for(int i=0;i<data.length();i++) {
        JSONObject jsonDay = data.getJSONObject(i);

        days[i].setSummary(jsonDay.getString("summary"));
        days[i].setTimeZone(timezone);
        days[i].setTime(jsonDay.getLong("time"));
        days[i].setIcon(jsonDay.getString("icon"));
        days[i].setTemperatureMax(jsonDay.getDouble("temperatureMax"));
    }
    return days;

}