Hello everyone! I used to define custom form widgets in odoo 10 as follow: 

var core = require('web.core');
var form_common = require('web.form_common');
var MyWidget = form_common.FormWidget.extend({
    init: function (parent, object) {
        console.log('INIT!!!');
        this._super.apply(this, arguments);
    },
    start: function () {
         //codes        
    },
    events: {
        "click button.ct_button_filter": "open_search_dialog",
    },
    open_search_dialog: function () {
        //codes...
    },
    display_filter: function () {
        //codes...
    },
});

core.form_custom_registry.add(
    'my_widget', MyWidget
);

and invoke it in this way:
...<page string="Details..."><widget type="my_widget"> </page>.....
This perfectly works in odoo 10; but in 11, I get this error: Widget is not a constructor.
Do you have any idea guys?