# A cached null is a real entry called NullValue

searchCachingNulls("xyz") returns null, called twice -> 1 invocations

  cache "nulls":
    key xyz        ->  null   [org.springframework.cache.support.NullValue]

The abstraction stores org.springframework.cache.support.NullValue.INSTANCE
so a hit on null is distinguishable from a miss. This is usually what you
want - it is the cheap defence against a hot lookup for a row that is not
there - and occasionally exactly what you do not want.

--- unless = "#result == null" ---
searchNullable("xyz") twice -> 2 invocations   <- the null was never stored
  cache "terms":
    (empty)