def validate_image_redirect(response):
    if not response:
        response.failure("Response object is empty")

    if "/media/default/" in response.url:
        response.failure(f"Stub image URL in image redirect: {response.url}")


class CacheValidator:
    def __init__(self):
        self._urls = set()

    def __call__(self, response):
        try:
            initial_response = response.history[0]
        except IndexError:
            initial_response = response
        cache_val = initial_response.headers.get("X-Cache")
        if initial_response.url not in self._urls:
            self._urls.add(initial_response.url)
            return
        if cache_val != "HIT":
            response.failure(f"No cache hit for URL: {initial_response.url}")