如何在django中防止‘没有用户名’？

# forms.py
from django import forms
from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth.models import User

class CustomUserCreationForm(UserCreationForm):
    class Meta:
        model = User
        fields = ('username', 'email', 'password1', 'password2')

    def clean_username(self):
        username = self.cleaned_data['username']
        if not username:
            raise forms.ValidationError("用户名不能为空")
        return username

# middleware.py
from django.http import HttpResponseBadRequest

class UsernameValidationMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        if 'username' not in request.POST:
            return HttpResponseBadRequest("用户名不能为空")
        response = self.get_response(request)
        return response

MIDDLEWARE = [
    # 其他中间件
    'your_app.middleware.UsernameValidationMiddleware',
]

# signals.py
from django.db.models.signals import pre_save
from django.dispatch import receiver
from django.contrib.auth.models import User

@receiver(pre_save, sender=User)
def check_username(sender, instance, **kwargs):
    if not instance.username:
        raise ValueError("用户名不能为空")

# apps.py
from django.apps import AppConfig

class YourAppConfig(AppConfig):
    name = 'your_app'

    def ready(self):
        import your_app.signals