无法使用扩展用户模型来满足Django表单

from django import forms
from django.contrib.auth.forms import UserCreationForm
from .models import CustomUser

class CustomUserCreationForm(UserCreationForm):
    # 添加扩展模型的字段
    custom_field = forms.CharField(max_length=100)

    class Meta:
        model = CustomUser
        fields = ('username', 'email', 'password1', 'password2', 'custom_field')

from django.shortcuts import render, redirect
from .forms import CustomUserCreationForm

def register(request):
    if request.method == 'POST':
        form = CustomUserCreationForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('success')
    else:
        form = CustomUserCreationForm()
    return render(request, 'register.html', {'form': form})