Can not read property 'get_file' of undefined

As I can solve this error, my code is:

odoo.define('backup_all', function (require) {
"use strict";

var core = require('web.core');
var Widget = require('web.Widget');
var framework = require('web.framework');

var web_settings_dashboard = require('web_settings_dashboard');
var crash_manager = require('web.crash_manager');


var DashboardBackups = Widget.extend({
    template: 'DashboardBackups',

    events: {
        'click .o_web_settings_dashboard_download_backup': 
'on_backup_clicked',
    },

    init: function(parent, data){
        this.data = data;
        this.parent = parent;
        this._super.apply(this, arguments);
    },

    on_backup_clicked: function(e){
        e.preventDefault();
        var filename = $(e.currentTarget).data('filename');
        framework.blockUI();
        var c = crash_manager;
        this.session.get_file({
            'url': '/odoo/backups',
            'data': {
                'filename': filename,
            },
            'complete': framework.unblockUI,
            'error': c.rpc_error.bind(c)
        });
        e.stopPropagation();
    },
});

The error is:

Uncaught TypeError: Cannot read property 'get_file' of undefined