We don't have to check if the file already exists here, since it's always in production mode (dev overrides the readBuildId method to always be `development`) If the file is not found (error is thrown) we check if the file exists. If not we throw a helpful error. In other cases we throw the original error.
Extracting the logic that defines if a page is blocked to utils.
If that refactor make sense, I will create a next PR to cover both of the functions inside utils with tests.