Still obtaining error 

```{python}
/usr/local/lib/python3.7/dist-packages/pymc3/backends/report.py in _run_convergence_checks(self, idata, model)
    139 
    140         warnings = []
--> 141         rhat_max = max(val.max() for val in rhat.values())
    142         if rhat_max > 1.4:
    143             msg = (

ValueError: max() arg is an empty sequence
```