GraphQL example for webonyx/graphql-php library

gistfile1.txt

<?php
require_once 'vendor/autoload.php';


use GraphQL\GraphQL;
use GraphQL\Type\Schema;
use GraphQL\Type\Definition\ObjectType;
use GraphQL\Type\Definition\Type;
use GraphQL\Server\StandardServer;
use Laminas\Diactoros\ServerRequestFactory;
use GraphQL\Server\ServerConfig;
use GraphQL\Error\DebugFlag;



$flats_item = new ObjectType(
    [
      'name' => 'FlatItem',
      'fields' => [
        'id'         => Type::int(),
        'floor'      => Type::int(),
        'num'        => Type::int(),
        'price'      => Type::int(),
        'area_total' => Type::int(),
        'complex'    => Type::string()
      ]
    ]
);

$flats_items = new ObjectType(
    [
      'name' => 'FlatsItems',
      'fields' => [
        'items' => Type::listof($flats_item)
      ]
    ]
);

$flats = [
    'type' => $flats_items,
    'args' => [
      'price_min' => Type::int(),
      'price_max' => Type::int(),
    ],
    'resolve' => function ($rootValue, $args) {
      
      $flats = [
          [
                  'id' => 1,
                  'floor' => 2,
                  'num' => 3,
                  'price' => 100,
                  'area_total' => 10,
                  'complex' => 'Complex 1'
          ],
          [
                  'id' => 2,
                  'floor' => 2,
                  'num' => 3,
                  'price' => 200,
                  'area_total' => 10,
                  'complex' => 'Complex 2'
          ],
          [
                  'id' => 3,
                  'floor' => 2,
                  'num' => 3,
                  'price' => 300,
                  'area_total' => 10,
                  'complex' => 'Complex 3'
          ],
          [
                  'id' => 3,
                  'floor' => 2,
                  'num' => 3,
                  'price' => 400,
                  'area_total' => 10,
                  'complex' => 'Complex 1'
          ],
      ];

      return ['items' => array_filter($flats,function($flat) use ($args) {
          
          if($flat['price']>$args['price_min'])
            return true;
          else
            return false;
        
      })];
    }
];

$query = new ObjectType([
  'name' => 'Query',
  'fields' => [
    'flats' => $flats,
  ]
]);

$schema = new Schema([
    'query' => $query,
]);



$server_config = ServerConfig::create()
->setSchema($schema);

$request = ServerRequestFactory::fromGlobals();

$rawInput = file_get_contents('php://input');

$input = json_decode($rawInput, true);

$request = $request->withParsedBody($input);

$server = new StandardServer($server_config);
$result = $server->executePsrRequest($request);

I follow this but I have an error. The schema does not define the required query root type.