def METHOD_NAME(self):
    """ Extract block size from filesystem info.
        :returns: block size of fileystem or None
        :rtype: :class:`~.size.Size` or NoneType
    """
    if self.fs._current_info is None:
        return None
    block_size = None
    for line in (l.strip() for l in self.fs._current_info.splitlines() if l.startswith("Block size:")):
        try:
            block_size = int(line.split(" ")[-1])
            break
        except ValueError:
            continue
    return Size(block_size) if block_size else None