问“NoneType”对象在某个项目上没有“username”属性，该项目已正常工作了一段时间

EN

Roles = (
('sales', 'SALES'),
('operations', 'OPERATIONS'),
('cashier', 'CASHIER'),
('frontdesk', 'FRONTDESK'),
('client', 'CLIENT'),

class UserProfile(models.Model):
user = models.OneToOneField(User,on_delete=models.CASCADE, default=None, null=True)
role = models.CharField(max_length=50, choices=Roles, default='client')
feedback = models.TextField(default=None, null=True)

def __str__(self):
    return self.user.username

@login_required
def feedback(request):
form = FeedbackForm()

if request.method =='POST':

    form = FeedbackForm(request.POST)
    if form.is_valid():
        form = FeedbackForm.save()
return render(request, 'NewApp/feedback.html',{'form':form})

class UserForm(forms.ModelForm):
    password = forms.CharField(widget=forms.PasswordInput())
    confirm_password = forms.CharField(widget=forms.PasswordInput())
    class Meta():
        model = User
        fields =   ('first_name','last_name','username','email','password')

    def clean(self):
        cleaned_data = super(UserForm, self).clean()
        password = cleaned_data.get("password")
        confirm_password = cleaned_data.get("confirm_password")

        if password != confirm_password:
            raise forms.ValidationError(
                "password and confirm_password does not match"
            )


class UserProfileInfoForm(forms.ModelForm):

    class Meta():
        model = UserProfile
        fields = ('role',)

class FeedbackForm(forms.ModelForm):
    class Meta():
        model = UserProfile 
        fields = ('feedback',)