Timestamp Microservice - cannot pass two test and need help

Hi, I am working on Timestamp Microservice and I can’t pass the two last tests:
-It should handle an empty date parameter, and return the current time in unix format
-It should handle an empty date parameter, and return the current time in UTC format

I can’t understand where my mistake is in my code and what am I not seeing. I would appreciate if somebody could take a look at it and let me know if they see a problem. Much thanks!

// server.js
// where your node app starts

// init project
var express = require('express');
var app = express();

// enable CORS (https://en.wikipedia.org/wiki/Cross-origin_resource_sharing)
// so that your API is remotely testable by FCC 
var cors = require('cors');
app.use(cors({optionSuccessStatus: 200}));  // some legacy browsers choke on 204

// http://expressjs.com/en/starter/static-files.html

// http://expressjs.com/en/starter/basic-routing.html
app.get("/", function (req, res) {
  res.sendFile(__dirname + '/views/index.html');

// your first API endpoint... 
app.get("/api/hello", function (req, res) {
  res.json({greeting: 'hello API'});

app.get('/api/timestamp/:date_string', function(req, res){
       let time;
       let regex = RegExp(/^\d*$/g);
      //this is the piece that is supposed to handle empty date parameters
       if(req.params.date_string === null){
         time = new Date(Date.now())
       }else if(regex.test(req.params.date_string)){
         time = new Date(parseInt(req.params.date_string, 10))
         time = new Date(req.params.date_string)
        res.json({'error': "Invalid Date" })
      else{res.json({"unix": time.getTime(), "utc": time.toUTCString()})}

// listen for requests :)
var listener = app.listen(process.env.PORT, function () {
  console.log('Your app is listening on port ' + listener.address().port);

Okay, I solved this by creating a separate endpoint for /api/timestamp.