public function createdBy($nullable = false)
    {
        $columnName = Config::get('culpa.default_fields.created');
        if (!$columnName) {
            throw new \Exception('No column for the created field is configured, did you publish the Culpa config?');
        }

        $field = $this->integer($columnName)->unsigned();

        if (true === $nullable) {
            $field->nullable();
        }

        $this->addCulpaForeign($columnName);

        return $field;
    }