code: public BlockMeta getBlockMeta(long blockId) throws BlockDoesNotExistException {
      BlockMeta blockMeta = mBlockIdToBlockMap.get(blockId);
      if (blockMeta == null) {
        throw new BlockDoesNotExistException(ExceptionMessage.BLOCK_META_NOT_FOUND, blockId);
      }
      return blockMeta;
    }
docs: Gets the {@link BlockMeta} from this storage dir by its block id.
  
  @param blockId the block id
  @return {@link BlockMeta} of the given block or null
  @throws BlockDoesNotExistException if no block is found