code: public function getItem($key)
      {
          if ($this->hasItem($key) !== true) {
              $this->data[$key] = new CacheItem($key, null, false);
          }
          
          return $this->data[$key];
      }
docs: Returns a Cache Item representing the specified key.
  
  This method must always return a CacheItemInterface object, even in case of
  a cache miss. It MUST NOT return null.
  
  @param string $key
  The key for which to return the corresponding Cache Item.
  
  @throws InvalidArgumentException If the $key string is not a legal value a \Psr\Cache\InvalidArgumentException
  MUST be thrown.
  
  @return CacheItemInterface