Bug fix: Sending an empty array to clear a dropdown column

We recently fixed a bug that now allows you to clear a dropdown column by sending an empty array in one of the following mutations:

mutation {
  change_multiple_column_values (item_id: 123456789, board_id: 987654321, column_values: "{\\"dropdown\\":{\\"ids\\":[]}}") {
    column_values (ids: dropdown) {
      id
      value
    }
  }
}

mutation {
  change_multiple_column_values (item_id: 123456789, board_id: 987654321, column_values: "{\\"dropdown\\":{\\"labels\\":[]}}") {
    column_values (ids: dropdown) {
      id
      value
    }
  }
}