An empty list kills normalize()

[aatifsyed]

import pandas as pd
import flat_table

df = pd.DataFrame([
  {"list_of_properties":[]}
])

flat_table.normalize(df=df, expand_dicts=True, expand_lists=False)

Will result in a series of errors. This might be valid for expand_lists=True, but is undesirable when only expanding dicts

[aatifsyed]

I suspect this is what caused #12