How To Grab Json File From External Url(PLACES API) Using Firebase Functions

So, I want to send a request from my app to Firebase using cloud funtions and then process process url and send back JSON file from places api

WHAT I HAVE ALREADY DONE/HAVE=> After Setting up the project in console and getting firebase CLI created a cloud function as follows

After following your comments this is my full function code:

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const rp = require('request-promise');

exports.fetch = functions.https.onCall((req, res) => {

    const url = req.url + '&key=MY_API_KEY';
    var options = {
        uri: url, // Automatically parses the JSON string in the response
        json: true
    };  

    rp(options)
    .then(result => {
        console.log('Get response:' + response.statusCode);
        return res.type('application/json').send(result);
    }).catch(err => {
        // API call failed...
        return res.send({'Error': err});
    });

})

and in java class passed values like this

     private Task<String> addMessage(String url) {
            // Create the arguments to the callable function.
            Map<String, Object> data = new HashMap<>();
            data.put("url", url);///PASSING VALUES HERE
            return mFunctions
                    .getHttpsCallable("fetch")
                    .call(data)
                    .continueWith(task -> 
(String) Objects.requireNonNull(task.getResult()).getData());
        }

Now What my problem is while deploying new function code with firebase CLI I am getting 16:8 error Each then() should return a value or throw promise/always-return as error

Can anyone guide me please..,

URL will be like this : https://maps.googleapis.com/maps/api/place/nearbysearch/json?location=17.4369681,78.4473887&radius=5000&type=airport&sensor=true&key=MY_KEY

Here are the log details from console

2019-07-05T10:06:35.025308453Z D fetch: Function execution started
2019-07-05T10:06:35.265840608Z D fetch: Function execution took 241 ms, finished with status code: 200
2019-07-05T10:06:45.162Z I fetch: Get response:undefined
2019-07-05T10:06:46.062Z E fetch: Unhandled rejection
2019-07-05T10:06:46.062Z E fetch: TypeError: res.send is not a function
    at rp.then.catch.err (/srv/index.js:22:14)
    at bound (domain.js:301:14)
    at runBound (domain.js:314:12)
    at tryCatcher (/srv/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/srv/node_modules/bluebird/js/release/promise.js:517:31)
    at Promise._settlePromise (/srv/node_modules/bluebird/js/release/promise.js:574:18)
    at Promise._settlePromise0 (/srv/node_modules/bluebird/js/release/promise.js:619:10)
    at Promise._settlePromises (/srv/node_modules/bluebird/js/release/promise.js:695:18)
    at _drainQueueStep (/srv/node_modules/bluebird/js/release/async.js:138:12)
    at _drainQueue (/srv/node_modules/bluebird/js/release/async.js:131:9)
    at Async._drainQueues (/srv/node_modules/bluebird/js/release/async.js:147:5)
    at Immediate.Async.drainQueues (/srv/node_modules/bluebird/js/release/async.js:17:14)
    at runCallback (timers.js:810:20)
    at tryOnImmediate (timers.js:768:5)
    at processImmediate [as _immediateCallback] (timers.js:745:5)

This worked for me., using return before promise returns the result from promise, and we need to use return when using functions.https.onCall and res.send when using functions.https.onRequest it took me 3 days to get it & no need of adding json=true in request-promise options when your url returns a json, it just made things complicated

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const rp = require('request-promise');

exports.fetch = functions.https.onCall((req, res) => {

    const url = req.url + '&key=MY_API_KEY';
    var options = {
        uri: url, // Automatically parses the JSON string in the response
    };

    return rp(options)
    .then(result => {
        console.log('here is response: ' + result);
        return result;
    }).catch(err => {
        // API call failed...
        return err;
    });

})