code: public @Nonnull T getOrCreate(String key, P createParams) throws IOException {
          return get(key,true,createParams);
      }
docs: Atomically gets the existing data object if any, or if it doesn't exist
  {@link #create(String,Object) create} it and return it.
  
  @return
  Item with the specified {@code key}.
  @param createParams
  Additional parameters needed to create a new data object. Can be null.
  @throws IOException Loading error