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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def confirm_login_allowed(self, user):
 """ Controls whether the given User may log in. This is a policy setting, independent of end-user authentication. This default behavior is to allow login by active users, and reject login by inactive users. If the given user cannot log in, this method should raise a ``forms.ValidationError``. If the given user may log in, this method should return None. """

        if not user.is_active:
            raise forms.ValidationError(
                self.error_messages['inactive'],
                code='inactive',
            )