Nullable `value` argument in `change_simple_column_value` mutation

In API version 2023-10, the value argument in the change_simple_column_value mutation is nullable to enable column value deletion.

To clear the column, simply pass null value in the value argument.

mutation {
  change_simple_column_value (board_id:1234567890, item_id:9876543210, column_id:"date", value:null) {
    id
  }
}