fix: Improve handling of few keywords for topics

app.py

@@ -172,7 +172,10 @@ def generate_plot(
                 cluster_keyword[label].append(cluster_words[most_descriptive[0]])
             if len(cluster_keyword[label]) == 1:
                 cluster_keyword[label] = cluster_keyword[label][0]
-            cluster_keyword[label] = ', '.join(cluster_keyword[label])
+            elif len(cluster_keyword[label]) == 0:
+                cluster_keyword[label] = '-'
+            elif len(cluster_keyword[label]) > 1:
+                cluster_keyword[label] = ', '.join(cluster_keyword[label])
         encoded_labels_keywords = [cluster_keyword[encoded_label] for encoded_label in encoded_labels]
         embeddings_2d = get_tsne_embeddings(embeddings)
     plot = draw_interactive_scatter_plot(