When run on local machine, i got 'TypeError: argument of type '_RequestGlobals' is not iterable'

from flask import (Flask, g, render_template, flash, redirect, url_for)
from flask.ext.login import LoginManager
import forms
import models

DEBUG = True
PORT = 8000
HOST = '0.0.0.0'

app = Flask(__name__)
app.secret_key = 'njgnbfdng!2fkgj9856&!jmbk[pln]wrtj,.kydaSHAPA'

login_manager = LoginManager()
login_manager.init_app(app)
login_manager.login_view = 'login'

@login_manager.user_loader
def load_user(userid):
    try:
        return models.User.get(models.User.id==userid)
    except models.DoesNotExist:
        return None



@app.before_request
def before_request():
    """Connect to the database before each request. """
    g.db = models.DATABASE
    g.db.connect(reuse_if_open=True)
    # g.db = models.DATABASE.connect()


@app.after_request
def after_request(response):
    """Close to the database after each request. """
    g.db.close()
    return response


@app.route('/register', methods=('GET', 'POST'))
def register():
    form = forms.RegisterForm()
    if form.validate_on_submit():
        flash("You registered!", 'success')
        models.User.create_user(
            username=form.username.data,
            email=form.email.data,
            password=form.password.data
        )
        return redirect(url_for('index'))
    return render_template('register.html', form=form)


@app.route('/')
def index():
    return 'Hey'

if __name__ == '__main__':
    models.initiatize()
    try:
        models.User.create_user(
            username="MoatazBellah",
            email="moatazbellah@gmail.com",
            password='123456',
            admin=True,
            bio='I am software engineer'
        )
    except ValueError:
        pass
    app.run(debug=DEBUG, host=HOST, port=PORT)

from flask_wtf import Form
from wtforms import StringField, PasswordField
from wtforms.validators import (DataRequired, Regexp, ValidationError, Email,
                                Length, EqualTo)
from models import User

# Function to check if the name already in exists
def name_exists(form, field):
    if User.select().where(User.username == field.data).exists():
        raise ValidationError('User already exists.')

# Function to check if the email already in exists
def email_exists(form, field):
    if User.select().where(User.email == field.data).exists():
        raise ValidationError('User already exists.')

# Create the Registeration class that contaoins username, email, password, password2
class RegisterForm(Form):
    username = StringField(
        'Username',
        validators=[
            DataRequired(),
            Regexp(
                r'^[a-zA-Z0-9_]+$',
                message='''Username should be one word,
                        letters, numbers, and underscores only'''
            ),
            name_exists
        ])
    email = StringField(
        'Email',
        validators=[
            DataRequired(),
            Email(),
            email_exists
        ])
    password = PasswordField(
        'Password',
        validators=[
            DataRequired(),
            Length(min=6),
            EqualTo('password2', message="Password must match")
        ])
    password2 = PasswordField(
        'Confirm Password',
        validators=[DataRequired()]
    )