我正在使用Python3开发一个Django项目。当我尝试创建一个新任务时，出现了这个错误。

django.db.utils.IntegrityError: NOT NULL constraint failed: tasks_task.user_id

web应用程序工作正常，但当我试图创建一个新任务是错误发生时，我已经阅读了所有与问题相关的帖子，但没有找到解决方案。
我试着更新我的sqlite3，但是没有用。
"这是我的准则"

from django.shortcuts import render, redirect
from django.contrib.auth.forms import UserCreationForm, AuthenticationForm
from django.contrib.auth.models import User
from django.contrib.auth import authenticate, login, logout
from django.db import IntegrityError
from .forms import TaskForm

def home(request):
    return render(request, 'home.html')

# Create your views here.

def signup(request):

    if request.method == 'GET':
        return render(request, 'signup.html', {
            'form': UserCreationForm
        })
    else:
        if request.POST['password1'] == request.POST['password2']:
            try:
                user = User.objects.create_user(
                    username=request.POST['username'], password=request.POST['password1'])
                user.save()
                login(request, user)
                return redirect('tasks')

            except IntegrityError:
                return render(request, 'signup.html', {
                    'form': UserCreationForm,
                    'error': 'Username already taken'
                })

        return render(request, 'signup.html', {
            'form': UserCreationForm,
            'error': 'Passwords did not match'
        })

def tasks(request):
    return render(request, 'tasks.html')

def create_task(request):
    if request.method == 'GET':
        return render(request, 'create_task.html', {
            'form': TaskForm,
        })
    else:
        try:
         form = TaskForm(request.POST)
         new_task = form.save(commit=False)
         new_task.User = request.user
         new_task.save()
         return redirect('tasks')
        except ValueError:
         return render(request, 'create_task.html', {
            'form': TaskForm,
            'error': 'Bad data passed in. Try again.'
        })

def signout(request):
    logout(request)
    return redirect('home')

def signin(request):
    if request.method == 'GET':
        return render(request, 'signin.html', {
            'form': AuthenticationForm
        })
    else:
        user = authenticate(
            request, username=request.POST['username'], password=request.POST['password'])
        if user is None:
            return render(request, 'signin.html', {
                'form': AuthenticationForm,
                'error': 'Username and password did not match'
            })
        else:
            login(request, user)
            return redirect('tasks')

"这是我的models.py“

from django.db import models
from django.contrib.auth.models import User

# Create your models here.

class Task(models.Model):
    title = models.CharField(max_length=200)
    description = models.TextField(blank=True)
    created = models.DateTimeField(auto_now_add=True)
    datecompleted = models.DateTimeField(null=True, blank=True)
    important = models.BooleanField(default=False)
    user = models.ForeignKey(User, on_delete=models.CASCADE)

    def __str__(self):
        return self.title + ' | ' + str(self.user)