# Buggy code
def tile(cls, op: "DataFrameDropNA"):
    in_df = op.inputs[0]
    out_df = op.outputs[0]

    if len(in_df.chunk_shape) == 1 or in_df.chunk_shape[1] == 1:
        return cls._tile_drop_directly(op)

    subset_df = in_df
    if op.subset:
        subset_df = in_df[op.subset]._inplace_tile()
    count_series = subset_df.agg(
        "count", axis=1, _use_inf_as_na=op.use_inf_as_na
    )._inplace_tile()

    nsplits, out_shape, left_chunks, right_chunks = align_dataframe_series(
        in_df, count_series, axis=0
    )
    out_chunk_indexes = itertools.product(*(range(s) for s in out_shape))

    out_chunks = []
    for out_idx, df_chunk in zip(out_chunk_indexes, left_chunks):
        series_chunk = right_chunks[out_idx[0]]
        kw = dict(
            shape=(np.nan, nsplits[1][out_idx[1]]),
            index_value=df_chunk.index_value,
            columns_value=df_chunk.columns_value,
        )

        new_op = op.copy().reset_key()
        new_op._drop_directly = False
        new_op._subset_size = len(op.subset) if op.subset else len(in_df.dtypes)
        out_chunks.append(
            new_op.new_chunk([df_chunk, series_chunk], index=out_idx, **kw)
        )

    new_op = op.copy().reset_key()
    params = out_df.params.copy()
    new_nsplits = list(tuple(ns) for ns in nsplits)
    new_nsplits[0] = (np.nan,) * len(new_nsplits[0])
    params.update(dict(nsplits=tuple(new_nsplits), chunks=out_chunks))
    return new_op.new_tileables(op.inputs, **params)


# Traceback (TypeError)
Traceback (most recent call last):
File "/Users/wenjun.swj/miniconda3/lib/python3.8/site-packages/IPython/core/interactiveshell.py", line 3417, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-9-60fd09690beb>", line 1, in <module>
df[df[0] > 0.5].execute()
File "/Users/wenjun.swj/Code/mars/mars/core.py", line 643, in execute
return run()
File "/Users/wenjun.swj/Code/mars/mars/core.py", line 639, in run
self.data.execute(session, **kw)
File "/Users/wenjun.swj/Code/mars/mars/core.py", line 379, in execute
return run()
File "/Users/wenjun.swj/Code/mars/mars/core.py", line 374, in run
session.run(self, **kw)
File "/Users/wenjun.swj/Code/mars/mars/session.py", line 505, in run
result = self._sess.run(*tileables, **kw)
File "/Users/wenjun.swj/Code/mars/mars/session.py", line 111, in run
res = self._executor.execute_tileables(tileables, **kw)
File "/Users/wenjun.swj/Code/mars/mars/utils.py", line 451, in _inner
return func(*args, **kwargs)
File "/Users/wenjun.swj/Code/mars/mars/executor.py", line 860, in execute_tileables
chunk_graph = chunk_graph_builder.build(
File "/Users/wenjun.swj/Code/mars/mars/utils.py", line 451, in _inner
return func(*args, **kwargs)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 347, in build
chunk_graph = super().build(
File "/Users/wenjun.swj/Code/mars/mars/utils.py", line 451, in _inner
return func(*args, **kwargs)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 262, in build
self._on_tile_failure(tileable_data.op, exc_info)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 301, in inner
raise exc_info[1].with_traceback(exc_info[2]) from None
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 242, in build
tiled = self._tile(tileable_data, tileable_graph)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 337, in _tile
return super()._tile(tileable_data, tileable_graph)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 201, in _tile
tds[0]._inplace_tile()
File "/Users/wenjun.swj/Code/mars/mars/core.py", line 168, in _inplace_tile
return handler.inplace_tile(self)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 136, in inplace_tile
dispatched = self.dispatch(to_tile.op)
File "/Users/wenjun.swj/Code/mars/mars/utils.py", line 451, in _inner
return func(*args, **kwargs)
File "/Users/wenjun.swj/Code/mars/mars/tiles.py", line 119, in dispatch
tiled = op_cls.tile(op)
File "/Users/wenjun.swj/Code/mars/mars/dataframe/indexing/getitem.py", line 273, in tile
return cls.tile_with_mask(op)
File "/Users/wenjun.swj/Code/mars/mars/dataframe/indexing/getitem.py", line 287, in tile_with_mask
align_dataframe_series(in_df, mask, axis='index')
File "/Users/wenjun.swj/Code/mars/mars/dataframe/align.py", line 713, in align_dataframe_series
index_splits, index_nsplits = _calc_axis_splits(left.index_value, right.index_value,
File "/Users/wenjun.swj/Code/mars/mars/dataframe/align.py", line 490, in _calc_axis_splits
right_splits = left_splits = [[c] for c in left_chunk_index_min_max]
TypeError: 'NoneType' object is not iterable

# Fixed code
def tile(cls, op: "DataFrameDropNA"):
    in_df = op.inputs[0]
    out_df = op.outputs[0]

    # series tiling will go here
    if len(in_df.chunk_shape) == 1 or in_df.chunk_shape[1] == 1:
        return cls._tile_drop_directly(op)

    subset_df = in_df
    if op.subset:
        subset_df = in_df[op.subset]._inplace_tile()
    count_series = subset_df.agg(
        "count", axis=1, _use_inf_as_na=op.use_inf_as_na
    )._inplace_tile()

    nsplits, out_shape, left_chunks, right_chunks = align_dataframe_series(
        in_df, count_series, axis=0
    )
    out_chunk_indexes = itertools.product(*(range(s) for s in out_shape))

    out_chunks = []
    for out_idx, df_chunk in zip(out_chunk_indexes, left_chunks):
        series_chunk = right_chunks[out_idx[0]]
        kw = dict(
            shape=(np.nan, nsplits[1][out_idx[1]]),
            dtypes=df_chunk.dtypes,
            index_value=df_chunk.index_value,
            columns_value=df_chunk.columns_value,
        )

        new_op = op.copy().reset_key()
        new_op._drop_directly = False
        new_op._subset_size = len(op.subset) if op.subset else len(in_df.dtypes)
        out_chunks.append(
            new_op.new_chunk([df_chunk, series_chunk], index=out_idx, **kw)
        )

    new_op = op.copy().reset_key()
    params = out_df.params.copy()
    new_nsplits = list(tuple(ns) for ns in nsplits)
    new_nsplits[0] = (np.nan,) * len(new_nsplits[0])
    params.update(dict(nsplits=tuple(new_nsplits), chunks=out_chunks))
    return new_op.new_tileables(op.inputs, **params)