code: DatanodeBlockInfo addBlockInfo(Block block,
        DatanodeBlockInfo replicaInfo) {
      return getBlockBucket(block).addBlockInfo(block, replicaInfo);
    }
docs: Add a replica's meta information into the map
  
  @param replicaInfo
  a replica's meta information
  @return previous meta information of the replica
  @throws IllegalArgumentException
  if the input parameter is null