Duplicate elements in a collection are removed

[hiroshinakasone0]

Steps to reproduce

item1 = Item.new(id: 1, name: 'Item1')
item2 = Item.new(id: 2, name: 'Item2')
item3 = Item.new(id: 3, name: 'Item3')
items = [item1, item2, item1, item3]

json.cache_collection! items do |item|
  json.id item.id
  json.name item.name
end

Expected results

[
  { "id": 1, "name": "Item1"},
  { "id": 2, "name": "Item2"},
  { "id": 1, "name": "Item1"},
  { "id": 3, "name": "Item3"}
]

Actual results

[
  { "id": 1, "name": "Item1"},
  { "id": 2, "name": "Item2"},
  { "id": 3, "name": "Item3"}
]

Environment

Ruby: 2.3.4
Rails: 5.0.0