Issue with MutationOccurrenceVisualization notebook

[Albaburi]

When I run JupyterLab's notebook MutationOccurrenceVisualization I get this error:

ValueError                                Traceback (most recent call last)
<ipython-input-19-5431d1030684> in <module>
      5         print(sample, amplicon, amplicon_data)
      6 
----> 7         max_entry = max(amplicon_data['sites'])  # corresponds to all mutations
      8 
      9         if max_entry not in amplicon_data['muts']:

ValueError: max() arg is an empty sequence

I don´t kwon how to solve this isseu.
This is my data, which I have obtained after running V-pipe and getting the cooc-test.json file.