我有一個(gè)自定義注冊表單SignupForm，用于檢查email自定義用戶對象是否存在CustomUser，如果存在則引發(fā)ValidationError。但是當(dāng)我嘗試提出錯(cuò)誤時(shí)，我得到了AttributeError at /accounts/signup/  Manager isn't available; 'auth.User' has been swapped for 'accounts.CustomUser'。這是我的代碼。forms.pyfrom django.contrib.auth.forms import UserCreationFormfrom django import formsfrom django.core.exceptions import ValidationErrorfrom django.contrib.auth import get_user_modelclass SignupForm(UserCreationForm):    def __init__(self, *args, **kwargs):        super(UserCreationForm, self).__init__(*args, **kwargs)    email = forms.CharField(        widget=forms.EmailInput(        attrs={            'class': 'input',            'placeholder': 'bearclaw@example.com'        }    ))    ...    # other fields (username and password)    ...    def clean(self):       User = get_user_model()       email = self.cleaned_data.get('email')       if User.objects.filter(email=email).exists():            raise ValidationError("An account with this email exists.")       return self.cleaned_dataviews.pyfrom django.urls import reverse_lazyfrom django.views.generic import CreateViewfrom .forms import SignupFormfrom .models import CustomUser...# other views and imports...class CustomSignup(CreateView):    form_class = SignupForm    success_url = reverse_lazy('login')    template_name = 'registration/signup.html'models.pyfrom django.db import modelsfrom django.contrib.auth.models import AbstractUserclass CustomUser(AbstractUser):    email = models.EmailField(unique=True)    def __str__(self):        return self.usernamesettings.pyAUTH_USER_MODEL = "accounts.CustomUser"我錯(cuò)過了什么？