code: public static Single<Boolean> set(String cacheKey, int index, Object value) {
          return set(CacheService.CACHE_CONFIG_BEAN, cacheKey, index, value);
      }
docs: update the value of the specified index
  
  @param cacheKey the key for the cached list.
  @param index    the index of the element you want to update.
  @param value    the new value for the element.
  @return true on success, false on failure.