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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 get_formset_form_class(self):
 """ Returns the form class for use in the formset. If a form_class attribute or change_fields is provided then a form will be constructed with that. Otherwise None is returned. """

        if self.form_class or self.change_fields:
            params = {'formfield_callback': self.formfield_for_dbfield}
            if self.form_class:
                fc = self.customize_form_widgets(self.form_class)
                params['form'] = fc
            if self.change_fields:
                params['fields'] = self.change_fields

            return model_forms.modelform_factory(self.model, **params)