Uncaught Error: Assertion Failed: Cannot delegate set


i face this error when saving data to api

Uncaught Error: Assertion Failed: Cannot delegate set(‘firstName’, a) to the ‘content’ property of object proxy <>: its ‘content’ is undefined

below is my code

import Ember from 'ember';

export default Ember.ObjectController.extend({
    isValid: Ember.computed(
        function() {
            return !Ember.isEmpty(this.get('email')) &&
            !Ember.isEmpty(this.get('firstName')) &&
            !Ember.isEmpty(this.get('lastName')) &&
        save: function() {
            if (this.get('isValid')) {
                var _this = this;
                this.get('model').save().then(function(friend) {
                    _this.transitionToRoute('friends.show', friend);
            } else {
                this.set('errorMessage', 'You have to fill all the fields');
        cancel: function() {


You haven’t declared any firstName variable in your controller.

So that, if you haven’t assigned a model (in your route) that has that variable there is no object where the setter can actually set the value of firstNamevariable.