Django 1.10错误，'NoneType'对象不可调用

我正在尝试为Django项目构建用户注册页面 .

我有一个名为 custom_user 的应用程序，其中 models.py 文件包含以下内容（除了导入）：

class CustomUserManager(BaseUserManager):
    def create_user(self, identifier, password, email, full_name, date_of_birth):
        user = self.model(
            identifier=identifier,
            email=self.normalize_email(email),
            full_name=full_name,
            date_of_birth=date_of_birth
        )
        user.set_password(password)
        user.save(using=self._db)

        return user

    def create_superuser(self, identifier, password, email, full_name, date_of_birth):
        # Almost same as previous method.

class CustomUser(AbstractBaseUser, PermissionsMixin):
    objects = CustomUserManager()

    USERNAME_FIELD = 'identifier'
    identifier = models.CharField(max_length=40, unique=True)

    email = models.EmailField(max_length=200, unique=True)
    full_name = models.CharField(max_length=200)
    date_of_birth = models.DateField()

    is_active = models.BooleanField(default=True)
    is_staff = models.BooleanField(default=False)

    REQUIRED_FIELDS = ['full_name', 'email', 'date_of_birth']

    def get_full_name(self):
        return self.full_name
    def get_short_name(self):
        return self.identifier

在另一个名为 sign_up 的应用中，注册视图显示为：

def index(request):
    if request.method == 'POST':
        form = CreateUserForm(request.POST)

        if form.is_valid():
            # Create the new user.
            manager = CustomUserManager()

            user = manager.create_user(
                form.cleaned_data['identifier'],
                form.cleaned_data['password'],
                form.cleaned_data['email'],
                form.cleaned_data['full_name'],
                form.cleaned_data['date_of_birth'],
            )

            return HttpResponseRedirect(reverse('sign_up:user_created'))
    else:
        form = CreateUserForm()

    return render(request, 'sign_up/index.html', {'form': form})

views.py 文件导入 CreateUserForm 类（放在 sign_up 目录的 forms.py 中）：

from django.forms import ModelForm
from custom_user.models import CustomUser

class CreateUserForm(ModelForm):
    class Meta:
        model = CustomUser
        fields = ['identifier', 'password', 'email', 'full_name', 'date_of_birth']

...最后，视图使用的模板包含：

<h1>Welcome to the signup page!</h1>

<form action="{% url 'sign_up:index' %}" method="post">
{% csrf_token %}
{{ form }}
<input type="submit" value="Sign up" />
</form>

提交表单（并且 form.is_valid() 似乎返回 True ）时，将显示错误消息 TypeError at /sign_up/ 'NoneType' object is not callable 而不是 user_created 视图 .

追溯：

文件“/Users/carltiden/anaconda/lib/python2.7/site-packages/django/core/handlers/exception.py”在内部39. response = get_response（request）File“/ Users / carltiden / anaconda / lib /python2.7/site-packages/django/core/handlers/base.py“in _get_response 187. response = self.process_exception_by_middleware（e，request）File”/Users/carltiden/anaconda/lib/python2.7/site- package / django / core / handlers / base.py“in _get_response 185. response = wrapped_callback（request，* callback_args，** callback_kwargs）file”/Users/carltiden/GitHub/a_project/a_project/sign_up/views.py“in index 24. form.cleaned_data ['date_of_birth']，文件“/Users/carltiden/GitHub/a_project/a_project/custom_user/models.py”in create_user 15. date_of_birth = date_of_birth Exception Type：TypeError at / sign_up / Exception Value：'NoneType '对象不可调用

（第15行是实际代码中的 date_of_birth=date_of_birth 行 . ）为什么会发生这种情况;我在这做错了什么？