Update app.py

app.py

@@ -112,7 +112,7 @@ df_cate = pd.DataFrame(categories)
 
 def reset_cate(df_categories):
     if df_categories.equals(df_cate):
-        df_categories = pd.DataFrame(columns=['topic', 'description', 'expert'])
+        df_categories = pd.DataFrame([['', '', '']], columns=['topic', 'description', 'expert'])
     else:
         df_categories = df_cate.copy()
     return df_categories