actions-on-google api.ai doesn't send body in POST request with nodejs and express

I'm trying to run the sillyNameMaker example from actions-on-google with api.ai, on my computer. I set up a nodejs server with express, and a ngrok tunneling. When I try to send a request with my agent on api.ai, my server receives the POST request, but the body appears to be empty. Is there anything i didn't set up properly?

Here is my index.js file:

'use strict';
var express = require('express')
var app = express()
const ApiAiAssistant = require('actions-on-google').ApiAiAssistant;

function sillyNameMaker(req, res) {
  const assistant = new ApiAiAssistant({request: req, response: res});

  // Create functions to handle requests here
  const WELCOME_INTENT = 'input.welcome';  // the action name from the API.AI intent
  const NUMBER_INTENT = 'input.number';  // the action name from the API.AI intent
  const NUMBER_ARGUMENT = 'input.mynum'; // the action name from the API.AI intent

  function welcomeIntent (assistant) {
    assistant.ask('Welcome to action snippets! Say a number.');
  }

  function numberIntent (assistant) {
    let number = assistant.getArgument(NUMBER_ARGUMENT);
    assistant.tell('You said ' + number);
  }

  let actionMap = new Map();
  actionMap.set(WELCOME_INTENT, welcomeIntent);
  actionMap.set(NUMBER_INTENT, numberIntent);
  assistant.handleRequest(actionMap);

  function responseHandler (assistant) {
    console.log("okok")
    // intent contains the name of the intent you defined in the Actions area of API.AI
    let intent = assistant.getIntent();
    switch (intent) {
      case WELCOME_INTENT:
        assistant.ask('Welcome! Say a number.');
        break;

      case NUMBER_INTENT:
        let number = assistant.getArgument(NUMBER_ARGUMENT);
        assistant.tell('You said ' + number);
        break;
    }
  }
  // you can add the function name instead of an action map
  assistant.handleRequest(responseHandler);
}


app.post('/google', function (req, res) {
  console.log(req.body);
  sillyNameMaker(req, res);
})


app.get('/', function (req, res) {
  res.send("Server is up and running.")
})


app.listen(3000, function () {
  console.log('Example app listening on port 3000!')
})

And the error I got:

TypeError: Cannot read property 'originalRequest' of undefined
    at new ApiAiAssistant (/Users/clementjoudet/Desktop/Dev/google-home/node_modules/actions-on-google/api-ai-assistant.js:67:19)
    at sillyNameMaker (/Users/clementjoudet/Desktop/Dev/google-home/main.js:8:21)

I'm trying to print req.body but it is undefined... Thanks in advance for your help.

via clemkoa