"java.lang.NullPointerException" Error

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

private GoogleApiClient mClient;
@BindView(R.id.timeLabel) TextView mTimeLabel;
@BindView(R.id.temperatureLabel) TextView mTemperatureLabel;
@BindView(R.id.humidityValue) TextView mHumidityValue;
@BindView(R.id.precipValue) TextView mPrecipValue;
@BindView(R.id.summaryLabel) TextView mSummaryLabel;
@BindView(R.id.iconImageView) ImageView mIconImageView;

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

    String apiKey = "78c372a8f6e218e7dc2ae502ccba4b9e";
    double latitude = 37.8267;
    double longitude = -122.423;
    String forecastUrl = "https://api.forecast.io/forecast/" + apiKey +
            "/" + latitude + "," + longitude;

    if (isNetworkAvaliable()) {
        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(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                try {
                    String k, jsonData = response.body().string();
                    Log.v(TAG, jsonData);
                    if (response.isSuccessful()) {
                        mCurrentWeather = getCurrentDetails(jsonData);
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                updateDisplay();
                            }
                        });
                    } else {
                        allertUserAboutError();
                    }
                } catch (IOException e) {
                    Log.e(TAG, "Execption Caught", e);
                } catch (JSONException e) {
                    Log.e(TAG, "Execption Caught", e);
                }

            }
        });
    } else {
        Toast.makeText(this, R.string.network_unavaliable_message, Toast.LENGTH_LONG).show();
    }
    Log.d(TAG, "Main UI code is running!");

    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
    mClient = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}

private void updateDisplay() {
    mTemperatureLabel.setText(mCurrentWeather.getTemperature()+"");

}

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

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

   // Log.i(TAG, "From JSON: " + currently);

    return currentWeather;
}

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

private void allertUserAboutError() {

    AlertDialogFragment dialog = new AlertDialogFragment();
    dialog.show(getFragmentManager(), "error_dialog");

}

@Override
public void onStart() {
    super.onStart();

    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
    mClient.connect();
    Action viewAction = Action.newAction(
            Action.TYPE_VIEW, // TODO: choose an action type.
            "Main Page", // TODO: Define a title for the content shown.
            // TODO: If you have web page content that matches this app activity's content,
            // make sure this auto-generated web page URL is correct.
            // Otherwise, set the URL to null.
            Uri.parse("http://host/path"),
            // TODO: Make sure this auto-generated app deep link URI is correct.
            Uri.parse("android-app://omoody.stormy/http/host/path")
    );
    AppIndex.AppIndexApi.start(mClient, viewAction);
}

@Override
public void onStop() {
    super.onStop();

    // ATTENTION: This was auto-generated to implement the App Indexing API.
    // See https://g.co/AppIndexing/AndroidStudio for more information.
    Action viewAction = Action.newAction(
            Action.TYPE_VIEW, // TODO: choose an action type.
            "Main Page", // TODO: Define a title for the content shown.
            // TODO: If you have web page content that matches this app activity's content,
            // make sure this auto-generated web page URL is correct.
            // Otherwise, set the URL to null.
            Uri.parse("http://host/path"),
            // TODO: Make sure this auto-generated app deep link URI is correct.
            Uri.parse("android-app://omoody.stormy/http/host/path")
    );
    AppIndex.AppIndexApi.end(mClient, viewAction);
    mClient.disconnect();
}