Ionic and Firebase .update(): Nested Arrays are not supported - firebase

Question

I'm having this issue while I'm trying to perform a crud update function. To put into context, this is an Ionic app with Firebase. This is an app in which the user will be able to create events and update them at a later stage if they want. However, I'm not being able to perform the update with the following error:
ERROR FirebaseError: Function DocumentReference.update() called with invalid data. Nested arrays are not supported (found in document Events/XWtRgH04iEG9IUIqMrgX)
Below are highlighted the function that will save an event after being updated and the service that contains the update function. Any help is greatly appreciated!
saveEvent(event) {
let id = event.id;
let evtSave = {
id: id,
createdAt: event['createdAt'],
createdBy: event['createdBy'],
updatedAt: Date.now(),
part: event['part'] || ['No participants'],
comments: event['comments'] || ['No comments'],
type: event['type'],
title: event['title'],
date: event['date'],
time: event['time'],
map: event['map'],
players: event['players'],
location: event['location'],
description: event['description'],
image: event['image']
};
console.log('saveEvent: ', evtSave);
this.eventServ.updateEvents(id, evtSave)
.then(res => {
this.searchEvents();
console.log('Event: ', res);
this.myAlert('Event successfully updated');
this.mode = 'listMode';
});
Below is the code contained in the service:
updateEvents(eventID, event){
return this.firestore.collection('Events').doc(eventID).update(({
id: event.id,
createdAt: event.date,
createdBy: event.createdBy,
updatedAt: Date.now(),
part: [event.part],
comments: [],
type: event.type,
title: event.title,
date: event.dateMilis,
time: event.time,
map: event.map,
players: event.players,
location: event.location,
description: event.description || 'No description...',
image: event.image || 'No image...',
})).catch((error)=>{
console.log('Error: ', error);
})
and finally a screenshot of how an event looks like in firebase:

Answer 1

At one place in your code you have part: event['part'] || ['No participants'], which will set part to an array of stringy, containing exactly one participant.
Later, when you save, you do: part: [event.part], which I assume can lead to the case where you will get part: [['No participants']].
This is a nested array and as firebase tells you in the error message, this is not supported in firestore.