code: def get_field_mapping(self):
          
          field_mapping = self.field_mapping_widget.get_field_mapping()
          for k, v in list(field_mapping['values'].items()):
              if not v:
                  field_mapping['values'].pop(k)
          for k, v in list(field_mapping['fields'].items()):
              if not v:
                  field_mapping['fields'].pop(k)
          return field_mapping
docs: Obtain metadata from current state of the widget.
  
          Null or empty list will be removed.
  
          :returns: Dictionary of values by type in this format:
              {'fields': {}, 'values': {}}.
          :rtype: dict