code: function readBuffer(pathOrBuffer) {
    if (typeof pathOrBuffer === 'string') {
      return promisify(fs.readFile)(pathOrBuffer).catch((error) => {
        throw new CustomError(m.errors.read_file, 'Could not read file (' + error.message + ')')
      })
    }
    if (typeof pathOrBuffer === 'object' && Buffer.isBuffer(pathOrBuffer)) {
      return Promise.resolve(pathOrBuffer)
    }
    return Promise.reject(new CustomError(m.errors.read_file, 'Not a file path or buffer'))
  }
docs: Transform the given input to a buffer
  (May be a string or a buffer)