wrong usage of LibCloudStorage._get_object in LibCloudStorage._read

[engAmirEng]

I bumped into this bug when I was trying to make LibCloudStorage work with django's ManifestFilesMixin but that doesn't matter and it should be fixed regardless.

exact version of what it is now:

def _get_object(self, name):
    """Get object by its name. [Return None if object not found"""
    clean_name = self._clean_name(name)
    try:
        return self.driver.get_object(self.bucket, clean_name)
    except ObjectDoesNotExistError:
        return None

def _read(self, name):
    obj = self._get_object(name)
    # TOFIX : we should be able to read chunk by chunk
    return next(self.driver.download_object_as_stream(obj, obj.size))

my recommendation:

def _read(self, name):
    obj = self._get_object(name)
    if obj is None:
        raise FileNotFoundError(f"{name} does not exist.")
    # TOFIX : we should be able to read chunk by chunk
    return next(self.driver.download_object_as_stream(obj, obj.size))

and if you are curious about the exact trigger of the bug:

class ManifestFilesMixin(HashedFilesMixin):
    def read_manifest(self):
        try:
            with self.manifest_storage.open(self.manifest_name) as manifest:
                return manifest.read().decode()
        except FileNotFoundError:
            return None