module ActionDispatch::Http::Cache::Response

def handle_conditional_get!
  # Normally default cache control setting is handled by ETag middleware. But, if
  # an etag is already set, the middleware defaults to `no-cache` unless a default
  # `Cache-Control` value is previously set. So, set a default one here.
  if (etag? || last_modified?) && !self._cache_control
    self._cache_control = DEFAULT_CACHE_CONTROL
  end
end