lineボット(python)で送られた文章を形態素解析し、単語の頻度を返すシステムが動作しない

前提・実現したいこと

lineボット(python)で送られた文章を形態素解析し、単語の頻度を返すシステムを作っています。
形態素解析を組み込んだ機能を実装中に動かなくなりました。

コードに間違えがあったら教えていただけると幸いです。よろしくお願いします。

該当のソースコード

from flask import Flask, request, abort

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage,
)
import os

import MeCab

app = Flask(__name__)


#環境変数取得
YOUR_CHANNEL_ACCESS_TOKEN = os.environ["YOUR_CHANNEL_ACCESS_TOKEN"]
YOUR_CHANNEL_SECRET = os.environ["YOUR_CHANNEL_SECRET"]

line_bot_api = LineBotApi(YOUR_CHANNEL_ACCESS_TOKEN)
handler = WebhookHandler(YOUR_CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        abort(400)

    return 'OK'


#----------------------------ここからMeCab
def WordFrequencyCount(word, WORD_FREQUENCY_COUNT):
    if word in WORD_FREQUENCY_COUNT:
        WORD_FREQUENCY_COUNT[word] +=1

    else:
        WORD_FREQUENCY_COUNT.setdefault(word, 1)
    return WORD_FREQUENCY_COUNT

def kaburizi(text):
    WORD_COUNT = []
    WORD_FREQUENCY_COUNT = {}
    #特定の品詞の単語を抽出
    mecab = MeCab.Tagger()
    mecab.parse('')
    node = mecab.parseToNode(text)
    while node:
        if node.feature.split(",")[0] == "名詞":
            word = node.surface
            WordFrequencyCount(word, WORD_FREQUENCY_COUNT)
        elif node.feature.split(",")[0] =="動詞":
            word = node.surface
            WordFrequencyCount(word, WORD_FREQUENCY_COUNT)
        elif node.feature.split(",")[0] == "形容詞":
            word = node.surface
            WordFrequencyCount(word, WORD_FREQUENCY_COUNT)
        elif node.feature.split(",")[0] == "形容動詞":
            word = node.surface
            WordFrequencyCount(word, WORD_FREQUENCY_COUNT)
        else:pass
        node = node.next
    #辞書リストを取り出し、降順に並び替え
    for item in WORD_FREQUENCY_COUNT.items():
        WORD_COUNT.append(item)
    wordcount_output = sorted(WORD_COUNT, key = lambda x:x[1], reverse=True)
    return wordcount_output
#----------------------------ここまでMeCab

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    push_text = event.message.text
    msg = "ホーン"
    line_bot_api.reply_message(
        event.reply_token,
        TextSendMessage(text=msg)
        )


if __name__ == "__main__":
#    app.run()
    port = int(os.getenv("PORT", 5000))
    app.run(host="0.0.0.0", port=port)