function encodeObjectId(op, columns) {
  if (op.obj === "_root") {
    columns.objActor.appendValue(null)
    columns.objCtr.appendValue(null)
  } else if (op.obj.actorNum >= 0 && op.obj.counter > 0) {
    columns.objActor.appendValue(op.obj.actorNum)
    columns.objCtr.appendValue(op.obj.counter)
  } else {
    throw new RangeError(
      `Unexpected objectId reference: ${JSON.stringify(op.obj)}`,
    )
  }
}
Encodes the `obj` property of operation `op` into the two columns
`objActor` and `objCtr`.