Firebase firestore cloud functions showing Error: Invalid use of type "undefined" as a Firestore argument

The error message is this:

Invalid use of type "undefined" as a Firestore argument.

You can see in your stack trace that this happens when you call set() with an object on a DocumentReference. It turns out that one of the values you're passing in the object is undefined. Check each of the values that you're passing and make sure all of them have an actual value:

 .set({
   id : id,
   branchName : branchName,
   currencyName : currencyName,
   sellingRate : sellingRate,
   buyingRate :buyingRate
  });

It's impossible to tell which one it is from the error message, so you'll have to print them all out do something to check each and every one of them.

When you .set an object but one of the fields in the object is undefined you will get this error.

The problem is that when you use console.log to display the object it does not show the undefined variables so it is difficult to trace.

Use the following instead of console.log to find the element that is causing the problem.

const util = require('util');
console.log(util.inspect(myObject, {showHidden: false, depth: null}));

This will give you an output as follows:

{ origin: 'AMS',
  destination: undefined,
  duration: 94,
  carrier: 'KL',
  flight_number: '2977',
  departure: '2019-06-11T15:34:00',
  arrival: '2019-06-11T17:08:00',
  type: 'flight' }