In version 9, I am trying to inherit the FieldBooleanButton object from web.form_widgets. It's telling me the object is undefined. I have no idea why. Here's my code:

odoo.define("custom_boolean_button.FieldBooleanButton", function(require) {
    "use strict";
    var form_widgets = require("web.form_widgets");
    form_widgets.FieldBooleanButton.include({
         // Do something
    });
});

I receive the error:

TypeError: Cannot read property 'include' of undefined