Add back Free user placeholder value after filtering out blacklisted users

app.py

@@ -17,7 +17,7 @@ def get_plot_df(df):
 
     # Filter out blacklisted users
     df["users"] = df["users"].apply(
-        lambda user_list: [u for u in user_list if u not in USER_BLACKLIST]
+        lambda user_list: [u for u in user_list if u not in USER_BLACKLIST] or ["Free"]
     )
 
     # Construct a new DataFrame for the bar chart