SWR Cache issues

Hi am getting a problem when i try to get the cache from the localStorage

This is my function like the swr docs

function localStorageProvider() {
  // When initializing, we restore the data from `localStorage` into a map.
  const map = new Map(JSON.parse(localStorage.getItem('app-cache') || '[]'))

  // Before unloading the app, we write back all the data into `localStorage`.
  window.addEventListener('beforeunload', () => {
    const appCache = JSON.stringify(Array.from(map.entries()))
    localStorage.setItem('app-cache', appCache)
  })

  // We still use the map for write & read for performance.
  return map
}

When i refresh the page i am getting the error of cannot read properties of undefined [0] .......

I already worked with swr cache before and didn't have any problems, maybe a version issue or something?

Thanks in advance