Symfony 4.2 deprecation warning (a tree builder without a root node is deprecated)

[nmeirik]

• Symfony version: 4.2
• Algolia Search Bundle version: 3.3.2
• Algolia Client Version: ??
• Language Version: ??

Description

After upgrading to Symfony 4.2, the following deprecation notice is thrown, seemingly related to this bundle:

A tree builder without a root node is deprecated since Symfony 4.2 and will not be supported anymore in 5.0.

[▼
  "exception" => SilencedErrorContext {#10588 ▼
    +count: 58
    -severity: E_USER_DEPRECATED
    trace: {▼
      /Users/eirik/code/nmproject/vendor/symfony/config/Definition/Builder/TreeBuilder.php:30 {▼
        › if (null === $name) {
        ›     @trigger_error('A tree builder without a root node is deprecated since Symfony 4.2 and will not be supported anymore in 5.0.', E_USER_DEPRECATED);
        › } else {
      }
      /Users/eirik/code/nmproject/vendor/algolia/search-bundle/src/DependencyInjection/Configuration.php:20 {▼
        › {
        ›     $treeBuilder = new TreeBuilder();
        ›     $rootNode = $treeBuilder->root('algolia_search');
      }
    }
  }
]

Here is the similar issue fixed for another bundle.

Steps To Reproduce

1. Install Symfony 4.2
2. Install algolia/search-bundle 3.3.2
3. Load up the application
4. Review the deprecation messages accessible from the web profiler toolbar

[01e9]

I fixed all warnings coming from my code, the rest are from algolia bundle
https://travis-ci.org/arteniioleg/defacto.md/builds/462507431#L568
Hoping for a soon fix

[alcaeus]

@arteniioleg #273 will fix this.