the two queries in the documentation for clearing the week and hour columns are no longer valid.

mutation {
  change_multiple_column_values(item_id:2973227073, board_id:2973227049, column_values: "{\\"week0\\":{ \\"week\\": {\\"startDate\\" : \\"\\", \\"endDate\\" : \\"\\"}}}") {
    id
  }
}

mutation {
  change_multiple_column_values(item_id: 2973227073, board_id: 2973227049, column_values: "{\\"hour\\" : {\\"hour\\" : \\"\\", \\"minute\\" : \\"\\"}}") {
    id
  }
}

both have changed to the following:

mutation {
  change_multiple_column_values(item_id: 2973227073, board_id: 2973227049, column_values: "{\\"columnid\\" : {}}") {
    id
  }
}