How can I convert request file to base64 encoded string in node js?

I using adonis.js

I try code like this :

import { HttpContextContract } from '@ioc:Adonis/Core/HttpContext'
const FileReader = require('file-reader');

export default class MyController {
  public async test({ request, response }: HttpContextContract) {;
    const fileToBase64 = async (file) =>
      new Promise((resolve, reject) => {
        const reader = new FileReader()
        reader.readAsDataURL(file)
        reader.onload = () => resolve(reader.result)
        reader.onerror = (e) => reject(e)
      })

    const file = request.file('files')
    const imageStr = await fileToBase64(file)
    return imageStr
  }
}

But if I run the function, there exist error like this :

invalid glob pattern: undefined

How can I solve this error?

The result reques.file('files') :

{
    "fieldName": "files[]",
    "clientName": "test.xlsx",
    "size": 8212,
    "type": "application",
    "extname": "xlsx",
    "subtype": "vnd.openxmlformats-officedocument.spreadsheetml.sheet",
    "state": "consumed",
    "isValid": true,
    "validated": true,
    "errors": [],
    "meta": {}
}