"TypeError: 'NoneType' object is not iterable" ERROR in Clustering

[gh-osh]

I've followed the exact method (for Kmean Clustering) you've written in the tutorial. But it generates following error:

100
iteration 1
100
iteration 2
69
iteration 3
48
iteration 4
38
Traceback (most recent call last):
  File "spatio-time cluster.py", line 177, in <module>
    for i in centroids:
TypeError: 'NoneType' object is not iterable

The datasets are same as your Github repo. I am also attaching the code. Please let me know, where I am doing wrong.