The API returns unclear 500 error when specified non existing user for mediaList

[temasaguru]

I tried to retrieve user mediaList with this query:

query ($userName: String) {
  Page {
    mediaList(userName: $userName) {
      media {
        title {
          romaji
          english
          native
          userPreferred
        }
        status
        episodes
      }
    }
  }
}

{
  "userName": "(non existing id here)"
}

However, when the specified user doesn't exist, this returns a 500 error without the cause of the error. I think returning 404 is more appriate.