am 16401ad4: Revert "sparse_img.py: Don\'t write empty map groups."

          nonzero_blocks.append(b)

          nonzero_blocks.append(b+1)

    assert zero_blocks or nonzero_blocks

    if zero_blocks:

      out["__ZERO"] = rangelib.RangeSet(data=zero_blocks)

    if nonzero_blocks:

      out["__NONZERO"] = rangelib.RangeSet(data=nonzero_blocks)

    out["__ZERO"] = RangeSet(data=zero_blocks)

    out["__NONZERO"] = RangeSet(data=nonzero_blocks)

  def ResetFileMap(self):

    """Throw away the file map and treat the entire image as