code: public StorageDir getDir(BlockStoreLocation location) {
      if (location.equals(BlockStoreLocation.anyTier())
          || location.equals(BlockStoreLocation.anyDirInTier(location.tierAlias()))) {
        throw new IllegalArgumentException(
            ExceptionMessage.GET_DIR_FROM_NON_SPECIFIC_LOCATION.getMessage(location));
      }
      return getTier(location.tierAlias()).getDir(location.dir());
    }
docs: Gets the {@link StorageDir} given its location in the store. Throws an
  {@link IllegalArgumentException} if the location is not a specific dir or the location is
  invalid.
  
  @param location Location of the dir
  @return the {@link StorageDir} object