src/Collection.php
public function merge($items)
    {
        if ($items instanceof CollectionInterface) {
            $items = $items->toArray();
        }

        if (!is_array($items)) {
            throw new InvalidArgumentException('Merge must be given array or Collection');
        }

        $this->validateItems($items, $this->type);
        $newItems = array_merge($this->items, $items);

        $col = new static ($this->type);
        $col->setItemsFromTrustedSource($newItems);

        return $col;
    }
public function merge($items)
    {
        if ($items instanceof CollectionInterface) {
            $items = $items->toArray();
        }

        if (!is_array($items)) {
            throw new InvalidArgumentException('Merge must be given array or Collection');
        }

        $this->validateItems($items, $this->type);
        $newItems = array_merge($this->items, $items);

        $col = new static ($this->type);
        $col->setItemsFromTrustedSource($newItems);

        return $col;
    }
{@inheritdoc}