Collection {#217 ▼

 #items: array:7 [▼

0 => {#397 ▼

  +"item_id": 1

  +"amount": "4"

}

1 => {#402 ▼

  +"item_id": 3

  +"amount": "1"

}

2 => {#396 ▶}

3 => {#213 ▶}

4 => {#399 ▶}

5 => {#400 ▶}

6 => {#398 ▶}

]

}

$union = $collection->union([2 => ['0']]);

$union = $collection->merge([2 => ['0']]);