code: @SuppressWarnings("unchecked")
      public <K, V> DataLoader<K, V> getDataLoader(String key) {
          return (DataLoader<K, V>) dataLoaders.get(key);
      }
docs: Returns the dataloader that was registered under the specified key
  
  @param key the key of the data loader
  @param <K> the type of keys
  @param <V> the type of values
  
  @return a data loader or null if its not present