Error caused by cluster_columns()

Anyone encounter the following error?
I have printed xs_imp before calling cluster_columns, it has normal, and seems correct output. is converted from 09_tabular.ipynb.

Traceback (most recent call last):
  File "/media/volgrp/myproject/git/AI/fastai/fastbook/", line 624, in <module>
  File "/root/anaconda3/lib/python3.8/site-packages/fastbook/", line 91, in cluster_columns
    hc.dendrogram(z, labels=df.columns, orientation='left', leaf_font_size=font_size)
  File "/root/anaconda3/lib/python3.8/site-packages/scipy/cluster/", line 3277, in dendrogram
    if labels and Z.shape[0] + 1 != len(labels):
  File "/root/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/", line 2149, in __nonzero__
    raise ValueError(
ValueError: The truth value of a Index is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().
Exception ignored in: <function Pool.__del__ at 0x7f79c3f50430>
Traceback (most recent call last):
  File "/root/anaconda3/lib/python3.8/multiprocessing/", line 268, in __del__
  File "/root/anaconda3/lib/python3.8/multiprocessing/", line 362, in put
AttributeError: 'NoneType' object has no attribute 'dumps'