digiaonline / graphql-php

src/Schema/Building/SchemaBuildingProvider.php

<?php

namespace Digia\GraphQL\Schema\Building;

use League\Container\ServiceProvider\AbstractServiceProvider;

class SchemaBuildingProvider extends AbstractServiceProvider
{
    /**
     * @var array
     */
    protected $provides = [
        SchemaBuilderInterface::class,
    ];

    /**
     * @inheritdoc
     */
    public function register()
    {
        $this->container->add(SchemaBuilderInterface::class, SchemaBuilder::class);

The method add() does not exist on Psr\Container\ContainerInterface. It seems like you code against a sub-type of Psr\Container\ContainerInterface such as League\Container\Container.

    }
}