Scenario:

 photo_id[]=1
 photo_caption[]=
 photo_id[]=2
 photo_caption[]=Hello

qs.parse returns:

{
     photo_id: ['1', '2'],
     photo_caption: ['Hello']
}

The correct version should be:

{
     photo_id: ['1', '2'],
     photo_caption: ['', 'Hello']
}

Otherwise, it's impossible to maintain associations between the ordered fields.