code: private BlockInfo getBlockInfo(long sessionId, long blockId) throws BlockDoesNotExistException {
      Key key = new Key(sessionId, blockId);
      BlockInfo blockInfo = mBlocks.get(key);
      if (blockInfo == null) {
        throw new BlockDoesNotExistException(ExceptionMessage.UFS_BLOCK_DOES_NOT_EXIST_FOR_SESSION,
            blockId, sessionId);
      }
      return blockInfo;
    }
docs: Gets the {@link UnderFileSystemBlockMeta} for a session ID and block ID pair.
  
  @param sessionId the session ID
  @param blockId the block ID
  @return the {@link UnderFileSystemBlockMeta} instance
  @throws BlockDoesNotExistException if the UFS block does not exist in the
  {@link UnderFileSystemBlockStore}