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