Basically to validate `object[property]` value not to be 
* null
* undefined
* NaN
* empty string ("")
* 0
* false

Since we are dealing with string values when working with REST, all these symptoms point to invalid value which should not be stored in cache.
In previous implementation we did this check on the "ouput":
```
if (cachedObject) {
    do something with cachedObject
}
```
but Jakob recommended to perform the validation BEFORE putting anything into cache, not AFTER, which sounds reasonable.