Unassign person from multiple-person column type via api

Hello,
I am trying to implement an option to unassign person from multiple-person column.
I tried to create this mutation:

      mutation {
        change_column_value (board_id: ${boardId}, item_id: ${itemId}, column_id: "person", value: ${user exist there ? null : {\\"personsAndTeams\\":[{\\"id\\":null,\\"kind\\":\\"person\\"}]}}) {
            id
        }
    }

While assigning working great, changing the value to null when there is already a user there, not working.

Any ideas? Thank you!