InvoiceShelf/app/Domains/Catalog/Http/Resources/UnitResource.php

<?php

namespace App\Domains\Catalog\Http\Resources;

use App\Domains\Accounts\Http\Resources\CompanyResource;
use Illuminate\Http\Request;
use Illuminate\Http\Resources\Json\JsonResource;

class UnitResource extends JsonResource
{
    /**
     * Transform the resource into an array.
     *
     * @param  Request  $request
     */
    public function toArray($request): array
    {
        return [
            'id' => $this->id,
            'name' => $this->name,
            'company_id' => $this->company_id,
            'company' => $this->when($this->company()->exists(), function () {
                return new CompanyResource($this->company);
            }),
        ];
    }
}