public function addField(FieldTypeInterface $field, SectionInterface $group): FieldsRepositoryInterface
    {
        // We store all fields together
        // as well as per group. On each form,
        // there is a "default" group defined where
        // all fields are attached to. A user can specify
        // a form group to the passed options on the "add"
        // method of the FormBuilder instance.
        $this->fields[$field->getBaseName()] = $field;
        $this->groups[$group->getId()] = $group;

        return $this;
    }