Ошибка при запуске flask и sql алхимии вместе

Question

Я получаю эти ошибки, когда пытаюсь запустить свое приложение, полагая, что оно как-то связано с тем, как я импортировал sqlalchemy, но не смог вставить в него пин-код. Я следую этому уроку: https://www.youtube.com/watch?v=cYWiDiIUxQc&list=PL-osiE80TeTs4UjLw5MM6OjgkjFeUxCYH&index=4

это ошибки, которые он мне дает введите описание изображения здесь

все они являются чем-то похожим на экземпляр sqlalchemy, не имеет члена столбца

вот мой код:

from datetime import datetime
from flask import Flask, render_template, url_for, flash, redirect
from flask_sqlalchemy import SQLAlchemy
from forms import RegistrationForm, LoginForm


app = Flask(__name__)
app.config['SECRET_KEY'] = 'thesecretkey'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'
db=SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(20), unique=True, Nullable=False)
    email = db.Column(db.String(120), unique=True, Nullable=False)
    image_file = db.Column(db.String(20), Nullable=False, default='default.jpg')
    password = db.Column(db.String(60), Nullable=False)
    posts = db.relationships('Post', backref='author', lazy=True)

    def __repr__(self):
        return f"User('{self.username}', '{self.email}', '{self.image_file}',)"

class Post(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100), nullable=False)
    date_posted = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    content = db.Column(db.text, nullable=False)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)

    def __repr__(self):
        return f"User('{self.title}', '{self.date_posted}')"

posts = [
    {
        'author': 'John Doe',
        'title': 'post 1',
        'content': 'first post content',
        'date': 'March 26, 2020'
    },
    {
        'author': 'Other Person',
        'title': 'post 2',
        'content': 'second post content' ,
        'date': 'March 26, 2020'         
    }
]




@app.route('/')
@app.route('/home')
def home():
    return render_template('home.html', posts=posts)

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

@app.route("/register", methods=['GET', 'POST'])
def register():
    form = RegistrationForm()
    if form.validate_on_submit():
        flash(f'Account created for {form.username.data}!', 'success')
        return redirect(url_for('home'))
    return render_template('register.html', title='Register', form=form)

@app.route('/login')
def login():
    form = LoginForm()
    return render_template('login.html', title = 'Login', form=form)

if __name__ == '__main__':
    app.run(debug=True)

вот ошибка, которая выдается мне при попытке запустить:

FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True or False to suppress this warning.
  warnings.warn(FSADeprecationWarning(
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Users/henrym/desktop/hello_flask/env/lib/python3.8/site-packages/flask/__main__.py", line 15, in <module>
    main(as_module=True)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 966, in main
    cli.main(prog_name="python -m flask" if as_module else None)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 586, in main
    return super(FlaskGroup, self).main(*args, **kwargs)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/click/decorators.py", line 73, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 848, in run_command
    app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 305, in __init__
    self._load_unlocked()
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 330, in _load_unlocked
    self._app = rv = self.loader()
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 392, in load_app
    app = locate_app(self, import_name, None, raise_if_not_found=False)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/flask/cli.py", line 240, in locate_app
    __import__(module_name)
  File "/Users/henrym/Desktop/hello_flask/app.py", line 12, in <module>
    class User(db.Model):
  File "/Users/henrym/Desktop/hello_flask/app.py", line 14, in User
    username = db.Column(db.String(20), unique=True, Nullable=False)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/sqlalchemy/sql/schema.py", line 1396, in __init__
    self._extra_kwargs(**kwargs)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/sqlalchemy/sql/schema.py", line 1399, in _extra_kwargs
    self._validate_dialect_kwargs(kwargs)
  File "/Users/henrym/Desktop/hello_flask/env/lib/python3.8/site-packages/sqlalchemy/sql/base.py", line 290, in _validate_dialect_kwargs
    raise TypeError(
TypeError: Additional arguments should be named <dialectname>_<argument>, got 'Nullable'
(env) Henrys-Air:hello_flask henrym$