当我访问路由时，为什么这会返回内部服务器错误500（'/ blogs'）

Question

当我通过路由/博客在浏览器中运行时，我收到内部服务器错误。这是什么意思，我怎么可能修复这个错误。运行其他路由时没有返回错误。

app.py：

from flask import Flask
from flask import render_template
from flask import request
from flask import session
from src.common.database import Database
from src.models.user import User

app = Flask(__name__)
app.secret_key = "Jongbin"


@app.route('/')
def home_template():
    return render_template('home.html')


@app.route('/login')
def login_template():
    return render_template('login.html')


@app.route('/register')
def register_template():
    return render_template('register.html')


@app.before_first_request
def initialise_database():
    Database.initialize()


@app.route('/auth/login', methods=['POST'])
def login_user():
    email = request.form['email']
    password = request.form['password']
    if User.login_valid(email, password):
        User.login(email)
    else:
        session['email'] = None
    return render_template("profile.html", email=session['email'])


@app.route('/auth/register', methods=['POST'])
def register_user():
    email = request.form['email']
    password = request.form['password']
    User.register(email, password)
    return render_template("profile.html", email=session['email'])


@app.route('/blogs/<string:user_id>')
@app.route('/blogs')
def user_blogs(user_id=None):
    if user_id is not None:
        user = User.get_by_id(user_id)
    else:
        user = User.get_by_email(session['email'])

    blogs = user.get_blogs()

    return render_template("user_blogs.html", blogs=blogs, email=user.email)


if __name__ == '__main__':
    app.run(port=4995)

user.py：

import uuid
import datetime
from flask import session
from src.common.database import Database
from src.models.blog import Blog


class User(object):
    def __init__(self, email, password, _id=None):
        self.email = email
        self.password = password
        self._id = uuid.uuid4().hex if _id is None else _id

    @classmethod
    def get_by_email(cls, email):
        data = Database.find_one("users", {'email': email})
        if data is not None:
            return cls(**data)
        return None

    @classmethod
    def get_by_id(cls, _id):
        data = Database.find_one("users", {'_id': _id})
        if data is not None:
            return cls(**data)

    @staticmethod
    def login_valid(email, password):
        user = User.get_by_email(email)
        if user is not None:
            return user.password == password
        return False

    @classmethod
    def register(cls, email, password):
        user = cls.get_by_email(email)
        if user is None:
            new_user = cls(email, password)
            new_user.save_to_mongo()
            session['email'] = email
            return True
        else:
            return False

    @staticmethod
    def login(user_email):
        session['email'] = user_email

    @staticmethod
    def logout():
        session['email'] = None

    def get_blogs(self):
        return Blog.find_by_author_id(self._id)

    def new_blog(self, title, description):
        blog = Blog(author=self.email,
                    title=title,
                    description=description,
                    author_id=self._id)
        blog.save_to_mongo()

    @staticmethod
    def new_post(blog_id, title, content, date=datetime.datetime.utcnow()):
        blog = Blog.from_mongo(blog_id)
        blog.new_post(title=title,
                      content=content,
                      date=date)

    def json(self):
        return {
            "email": self.email,
            "_id": self._id,
            "password": self.password
        }

    def save_to_mongo(self):
        Database.insert("users", self.json())