Flaskにおいて、"View function did not return a response"と表示されてしまう。

はじめまして。
現在以下の記事を参考に、Flaskを用いてinstagramユーザーの性別を推定しようと試みているのですが、エラーが出てしまいます。
http://codezine.jp/article/detail/8953

#エラー文
Traceback (most recent call last)
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/app.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/app.py", line 1478, in full_dispatch_request
response = self.make_response(rv)
File "/Users/Ryosuke/anaconda/lib/python3.5/site-packages/flask/app.py", line 1566, in make_response
raise ValueError('View function did not return a response')
ValueError: View function did not return a response

実際過去に私と同じようなエラーを発生している事例(http://stackoverflow.com/questions/25034123/flask-value-error-view-function-did-not-return-a-response)を見つけ、関数の最後にreturnを明示しなければならないことは分かったのですが、今回のコードではどこにreturnを明記してやればいいのか分かりません。

今回の場合、以下main.pyのどこにreturnを明記してやればよいでしょうか?
是非ともご教示のほどよろしくお願い致します。

python
1#main.py
2import os
3from flask import Flask, render_template, request
4from settings import instgram_access_token
5from api import InstagramAPI
6import pandas as pd
7from sklearn.externals import joblib
8
9app = Flask(__name__)
10
11@app.route("/", methods=['GET', 'POST'])
12def index():
13    try:
14        if request.method == 'POST': # POST応答
15            if request.form['message'] == '': #例外処理：ユーザー名未入力時
16                message = "Please input your Instagram User name in the box"
17                return render_template('index.html', title="Your gender?", method=request.method, message=message)
18            else:
19                message = "Your Instagram data"
20                insta = InstagramAPI(access_token=instgram_access_token)
21                user_name = request.form['message'] # ユーザー名を変数に代入
22                user_id = insta.user_id(user_name=user_name) # ユーザー名からユーザーIDを取得
23                profile_image = insta.profile_image(user_id) # プロフィール画像を取得
24                user = {'user_name': user_name, 'user_id': user_id, 'image': profile_image} # ユーザー情報をまとめる
25                user_summary = insta.user_info(user=user)
26                # 特徴量ベクトルの整理
27                test = {'nail': 0, 'hair': 0, 'person': 0, 'sport': 0, 'food': 0, 'night': 0, 'coffee': 0,
28                        'wedding': 0, 'cake': 0, 'beer': 0, 'dog': 0, 'animal': 0, 'tree': 0, 'blossom': 0,
29                        'cat': 0, 'flower': 0, 'sky': 0, 'nature': 0, 'cherry': 0, "user_name": "test", "user_id": "test"}
30                X = pd.DataFrame([user_summary, test]).fillna(0)
31                X['animal'] = X['animal']+X['dog']+X['cat']
32                X['cosme'] = X['hair']+X['nail']
33                X['nature'] = X['nature']+X['sky']+X['flower']+X['tree']+X['blossom']+X['cherry']
34                X = X[X['user_name'] == user_name]
35                X = X[['person', 'sport', 'food', 'night', 'coffee', 'wedding', 'cake', 'beer', 'animal', 'nature', 'cosme']]
36                user_vec = X.values.tolist()[0]
37
38                model_path = os.path.join(os.path.dirname(__file__), "clf/clf.pkl")
39                clf = joblib.load(model_path) # 識別器の読み込み
40                result = clf.predict(user_vec) # 性別推定
41
42                return render_template('index.html', title="Your gender?", method=request.method, userinfo=user_summary, result=result, message=message)
43        else: # GET応答
44            return render_template('index.html', title="Your gender?", method=request.method)
45
46    except Exception as e:
47        print(e)
48
49
50if __name__ == "__main__":
51    port = int(os.environ.get("PORT", 5000))
52    app.run(debug=True, port=port, host='IPアドレス省略')
53