code: def restore_default_button_clicked(self, classification):
          
          # Obtain default value
          class_dict = {}
          for the_class in classification.get('classes'):
              class_dict[the_class['key']] = {
                  'numeric_default_min': the_class['numeric_default_min'],
                  'numeric_default_max': the_class['numeric_default_max'],
              }
          # Set for all threshold
          for key, value in list(self.threshold_classes.items()):
              value[0].setValue(class_dict[key]['numeric_default_min'])
              value[1].setValue(class_dict[key]['numeric_default_max'])
docs: Action for restore default button clicked.
  
          It will set the threshold with default value.
  
          :param classification: The classification that being edited.
          :type classification: dict