error when there's no population data to display

[savitakartik]

In the Mutations page, I'm creating this dataframe to display the population frequency information:

df = pd.DataFrame(
    {
        "population": [
            pop.replace("pop_", "").replace("_freq", "") for pop in pops
        ],
        "frequency": [mut_data[col] for col in pops],
    }
)
df = df[df["frequency"] > 0]

and then I filter it so that we don't display populations with 0 frequency of mutation.
df = df[df["frequency"] > 0]
When the dataframe is empty then this line seems to cause an error at this line:
title=f"Mutation {mut_data['id']}"

Should check if df is empty before making the plot.

[savitakartik]