UnionType

error.json

{
   "errors":[
      {
         "message":"An unknown error occurred.",
         "location":[
            {
               "line":56,
               "column":5
            }
         ],
         "class":"GraphQL\\Error\\InvariantViolation",
         "debug":"Cannot return null for non-nullable field __InputValue.type."
      }
   ]
}

SearchQuery.php

<?php

namespace App\GraphQL\Query;

use GraphQL;
use GraphQL\Type\Definition\Type;
use GraphQL\Type\Definition\UnionType;
use Rebing\GraphQL\Support\Query;
use Rebing\GraphQL\Support\SelectFields;

class SearchQuery extends Query
{
    /**
     * The attributes that define this query.
     *
     * @var array
     */
    protected $attributes = [
        'name' => 'search',
    ];

    /**
     * This query returns a list of search results.
     *
     * @return GraphQL\Type\Definition\ListOfType
     */
    public function type()
    {
        return Type::listOf(new UnionType([
            'name' => 'SearchResult',
            'types' => [
                GraphQL::type('User'),
                GraphQL::type('Deal'),
            ],
            'resolveType' => function($value) {
                if ($value->type === 'user') {
                    return GraphQL::type('user');
                } else {
                    return GraphQL::type('venue');
                }
            }
        ]));
    }

    /**
     * The arguments that are available for this query.
     *
     * @return array
     */
    public function args(): array
    {
        return [
            'query' => [
                'name' => 'query',
                'Type' => Type::string(),
            ],
        ];
    }

    /**
     * Load the query response.
     *
     * @param       $root
     * @param array $args
     * @return mixed
     */
    public function resolve($root, array $args, SelectFields $fields)
    {
        dd($root, $args, $fields);
    }
}