code: public DataLoader<K, V> clear(K key) {
          Object cacheKey = getCacheKey(key);
          synchronized (this) {
              futureCache.delete(cacheKey);
          }
          return this;
      }
docs: Clears the future with the specified key from the cache, if caching is enabled, so it will be re-fetched
  on the next load request.
  
  @param key the key to remove
  
  @return the data loader for fluent coding