Android : android-fb-sdk email is always null

I have a big problem with android-facebook-sdk 3.19.1. No problem to retrieve public information about user but it is not possible getting email address.

I know my post is very near to the following thread ==> facebook android sdk -user email returns null but I have no solution for now.

So here is my code

In my ConnectionActivity.java I have a button R.id.fb_connect

private List<String> permissions = Arrays.asList("email");

@Click(R.id.fb_connect)
protected void fbConnect() {
    ensureOpenSession();
}

private boolean ensureOpenSession() {
    Session session = Session.getActiveSession();
    if (session == null || !session.isOpened()) {
        LOGD(TAG, "Call Session.openActiveSession");
        Session.openActiveSession(this, true, permissions, new FbCallback());
        return false;
    }
    return true;
}

public class FbCallback implements Session.StatusCallback {

    @Override
    public void call(Session session, SessionState sessionState, Exception e) {
        // make request to the /me API
        Request.newMeRequest(session, new Request.GraphUserCallback() {
            // callback after Graph API response with user object
            @Override
            public void onCompleted(GraphUser user, Response response) {
                if (user != null) {
                    // user.asMap().get("email");
                    Toast.makeText(ConnectionActivity.this, "email : " + user.getProperty("email"), Toast.LENGTH_LONG).show();
                }
            }
        }).executeAsync();
    }
}

I've also tried the code in the link above but it doesn't work.

Thx