Memcached c#: Should we store null object in memcached?

In case of object missing in the database, should we store "null" object in the Memcached.

Suppose, we have a 1 million product pages cached.

The product page has:

  1. Product basic info like price, location etc. in cacheBasic_productId.
  2. Product certification in cacheCertification_productId

Now, only 1K product have certification. Should we save a null object in the cache for rest of the product's certification?

If we start saving it's like saving too many unwanted keys with null object BUT if we don't do that, we will have to hit the database everytime to check the certification for these.

Any better solution i.e. how should null objects be saved/managed in cache?