code: public String getBlockPath(long blockId, BlockStoreLocation location) {
      return AbstractBlockMeta.commitPath(getDir(location), blockId);
    }
docs: Returns the path of a block given its location, or null if the location is not a specific
  {@link StorageDir}. Throws an {@link IllegalArgumentException} if the location is not a
  specific {@link StorageDir}.
  
  @param blockId the id of the block
  @param location location of a particular {@link StorageDir} to store this block
  @return the path of this block in this location