### What problem does this PR solve?
Sometimes, the **s** in **chunks (s, a)** is an empty string. This
causes the condition **if s and len(a) > 0** in the line **chunks = [(s,
a) for s, a in chunks if s and len(a) > 0]** to fail, which changes the
length of the new chunks. As a result, the final assertion **assert
len(chunks) - end == n_clusters, "{} vs. {}".format(len(chunks) - end,
n_clusters)** fails and raises a confusing error like 7 vs. 8
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):
e54c0e39b5