Update app.py

app.py

@@ -13,7 +13,7 @@ def huff_model_probability(df_distances, df_attractiveness, alpha, beta, df_popu
         df_population = pd.Series(np.ones(df_distances.shape[0]), index=df_distances.index)
 
     adjustment_factors = pd.DataFrame(index=df_distances.index, columns=df_distances.columns)
-    if distance_threshold is not None:
+    if distance_threshold is not None and distance_threshold is not "None":
         # Calculate adjustment factors for each origin-destination pair
         for destination in df_distances.columns:
             adjustment_factors[destination] = df_distances[destination].apply(