Paypal api – foreach is returning empty

I have a little doubt about a loop that I am doing, because it is returning empty values.

First, I am receiving my items like this:

$items = Session::get('items');
$deco = json_decode($items, true);

If I return $deco I get this:

{
 "items":[
      {
        "id":1,
        "inventoryID":1,
        "title":"Product 1",
        "quantity":1,
        "unit_price":20,
        "image":"img.png"
      },

      {
        "id":2,
        "inventoryID":1,
        "title":"Product2",
        "quantity":1,
        "unit_price":25,
        "image":"img.png"
       }
    ]
}

Now, in the loop (which I use to change the values of some keys for the integration of paypal) I have this:

$results = [];
    foreach($deco['items'] as $element) {

        $name=$element['title'];
        $quantity=$element['quantity'];
        $sku= $element['id'];
        $price=$element['unit_price'];


        $item = new Item();
        $item -> setName($name)
        ->setCurrency('USD')
        ->setQuantity($quantity)
        ->setSku($sku) 
        ->setPrice($price);

        $results[]=$item;
    }  

If I return return $item(outside the loop) I get (as expected) only one value, and not all of the collection:

{
"name": "Product2",
"currency": "USD",
"quantity": 1,
"sku": 2,
"price": "25"
}

But if I return return $results the var that I need, it gives me this (it does the {} of the items as I need, but returns empty):

[
{},
{}
]

Thw whole code looks like:

public function test(){
    $items = Session::get('items');
    $deco = json_decode($items, true);
    $results = [];
    foreach($deco['items'] as $element) {

        $name=$element['title'];
        $quantity=$element['quantity'];
        $sku= $element['id'];
        $price=$element['unit_price'];


        $item = new Item();
        $item -> setName($name)
        ->setCurrency('USD')
        ->setQuantity($quantity)
        ->setSku($sku) 
        ->setPrice($price);

        $results[]=$item;
    }  
    return $results;
}

EDIT: The Item.php model at vendorpaypalrest-api-sdk-phplibPayPalApi is the default PayPal’s:

class Item extends PayPalModel
{
/**
 * Stock keeping unit corresponding (SKU) to item.
 *
 * @param string $sku
 * 
 * @return $this
 */
public function setSku($sku)
{
    $this->sku = $sku;
    return $this;
}

/**
 * Stock keeping unit corresponding (SKU) to item.
 *
 * @return string
 */
public function getSku()
{
    return $this->sku;
}

/**
 * Item name. 127 characters max.
 *
 * @param string $name
 * 
 * @return $this
 */
public function setName($name)
{
    $this->name = $name;
    return $this;
}

/**
 * Item name. 127 characters max.
 *
 * @return string
 */
public function getName()
{
    return $this->name;
}

/**
 * Description of the item. Only supported when the `payment_method` is set to `paypal`.
 *
 * @param string $description
 * 
 * @return $this
 */
public function setDescription($description)
{
    $this->description = $description;
    return $this;
}

/**
 * Description of the item. Only supported when the `payment_method` is set to `paypal`.
 *
 * @return string
 */
public function getDescription()
{
    return $this->description;
}

/**
 * Number of a particular item. 10 characters max.
 *
 * @param string $quantity
 * 
 * @return $this
 */
public function setQuantity($quantity)
{
    $this->quantity = $quantity;
    return $this;
}

/**
 * Number of a particular item. 10 characters max.
 *
 * @return string
 */
public function getQuantity()
{
    return $this->quantity;
}

/**
 * Item cost. 10 characters max.
 *
 * @param string|double $price
 * 
 * @return $this
 */
public function setPrice($price)
{
    NumericValidator::validate($price, "Price");
    $price = FormatConverter::formatToPrice($price, $this->getCurrency());
    $this->price = $price;
    return $this;
}

/**
 * Item cost. 10 characters max.
 *
 * @return string
 */
public function getPrice()
{
    return $this->price;
}

/**
 * 3-letter [currency code](https://developer.paypal.com/docs/integration/direct/rest_api_payment_country_currency_support/).
 *
 * @param string $currency
 * 
 * @return $this
 */
public function setCurrency($currency)
{
    $this->currency = $currency;
    return $this;
}

/**
 * 3-letter [currency code](https://developer.paypal.com/docs/integration/direct/rest_api_payment_country_currency_support/).
 *
 * @return string
 */
public function getCurrency()
{
    return $this->currency;
}
//More similar stuff

Thank you in advance