title: why guava cache can only store non-null value in local cache and how to bypass this
body: <p>i'm adding local cache to my server by using google's guava utils.</p>
  
  <p>guava is very suitable for my scenario, except it can only store "non-null" values into its local cache (both com.google.common.cache.Cache and com.google.common.cache.LoadingCache did). </p>
  
  <p>well, this is not good. because my server may fail to get values from remote database, because of time run out or other reasons. if i give a default value to guava, it will be stored in local cache, and will always be there, unless some eviction conditions were met. but the question is i cannot give a reasonable default value to guava.</p>
  
  <p>can somebody tell me, why guava has this constraint, and how can i bypass it? can ehcache be more suited for my case?</p>