Incorrect ramping if target is omitted

[artych]

export let options = {
  stages: [
    {duration: '30s', target: 20},
    {duration: '30s', target: 10},
    {duration: '15s'},
    {duration: '30s', target: 20},
    {duration: '15s'},
    {duration: '15s', target: 10}
  ]
};