docs: def customize_form_widgets(self, form_class, fields=None):
          """
          Hook for customizing widgets for a form_class. This is needed
          for forms that specify their own fields causing the
          default db_field callback to not be run for that field.
  
          Default implementation checks for APIModelChoiceWidgets
          or APIManyChoiceWidgets and runs the update_links method
          on them. Passing the admin_site and request being used.
  
          Returns a new class that contains the field with the initialized
          custom widget.
          """
          attrs = {}
          if fields:
              fields = set(fields)
  
          for k, f in form_class.base_fields.items():
              if fields and not k in fields:
                  continue
  
              if isinstance(f.widget, widgets.APIModelChoiceWidget) \
                      or isinstance(f.widget, widgets.APIManyChoiceWidget):
                  field = copy.deepcopy(f)
                  field.widget.update_links(self.request, self.bundle.admin_site)
                  attrs[k] = field
  
          if attrs:
              form_class = type(form_class.__name__, (form_class,), attrs)
  
          return form_class