Django LoginView（）返回一个Nonetype

Question

这是观点：

   class LoginView(View):
    def get(self,request):
        return render(request,'login.html',{})
    def post(self,request):
        login_form = LoginForm(request.POST)
        if login_form.is_valid():
            user_name = request.POST.get("username", '')
            pass_word = request.POST.get("password", '')

            user = authenticate(username=user_name, password=pass_word)
            if user is not None:
                login(request, user)
                return render(request, 'index.html') 
        else:
            return render(request, 'login.html', {"msg": "User name or password error!"})

这是表格：

class LoginForm(forms.Form):
    username = forms.CharField(required=True)  
    password = forms.CharField(required=True, min_length=5) 

这是login_form返回NoneType的登录验证，我返回NoneType是否登录提交任何参数._bound_fields_cache是​​None，_errors是None.So我应该写什么？