How does nest-winston get rid of escaping quotes when building JSON.stringify()?

Question

How does nest-winston get rid of escaping quotes when building JSON.stringify()?

winston.config.ts:

  errors: {
    level: 'error',
    // filename: "./logs/errors.log",
    filename: pathErrors,
    handleRejections: true,
    handleExceptions: true,
    prettyPrint: true,
    json: true,
    maxsize: 5242880, // 5MB
    maxFiles: 5,
}

json: true or false does not affect in any way.