Symfony 3.4.0 has just been released. Here is a list of the most important changes:

• bug #25220 [HttpFoundation] Add Session::isEmpty(), fix MockFileSessionStorage to behave like the native one (@nicolas-grekas)
• bug #25209 [VarDumper] Dont use empty(), it chokes on eg GMP objects (@nicolas-grekas)
• bug #25200 [HttpKernel] Arrays with scalar values passed to ESI fragment renderer throw deprecation notice (@Simperfit)
• bug #25201 [HttpKernel] Add a better error messages when passing a private or non-tagged controller (@Simperfit)
• bug #25217 [Dotenv] Changed preg_match flags from null to 0 (@deekthesqueak)
• bug #25180 [DI] Fix circular reference when using setters (@nicolas-grekas)
• bug #25204 [DI] Clear service reference graph (@nicolas-grekas)
• bug #25203 [DI] Fix infinite loop in InlineServiceDefinitionsPass (@nicolas-grekas)
• bug #25185 [Serializer] Do not cache attributes if attributes in context (@sroze)
• bug #25190 [HttpKernel] Keep legacy container files for concurrent requests (@nicolas-grekas)
• bug #25182 [HttpFoundation] AutExpireFlashBag should not clear new flashes (@Simperfit, @sroze)
• bug #25174 [Translation] modify definitions only if the do exist (@xabbuh)
• bug #25179 [FrameworkBundle][Serializer] Remove YamlEncoder definition if Yaml component isn't installed (@ogizanagi)
• bug #25160 [DI] Prevent a ReflectionException during cache:clear when the parent class doesn't exist (@dunglas)
• bug #25163 [DI] Fix tracking of env vars in exceptions (@nicolas-grekas)
• bug #25162 [HttpKernel] Read $_ENV when checking SHELL_VERBOSITY (@nicolas-grekas)
• bug #25158 [DI] Remove unreachable code (@GawainLynch)
• bug #25152 [Form] Don't rely on SymfonyComponentHttpFoundationFileFile if http-foundation isn't in FileType (@issei-m)
• bug #24987 [Console] Fix global console flag when used in chain (@Simperfit)
• bug #25137 Adding checks for the expression language (@weaverryan)
• bug #25151 [FrameworkBundle] Automatically enable the CSRF protection if CSRF manager exists (@sroze)
• bug #25043 [Yaml] added ability for substitute aliases when mapping is on single line (@Michał Strzelecki, @xabbuh)

Want to upgrade to this new release? Fortunately, because Symfony protects backwards-compatibility very closely, this should be quite easy. Read our upgrade documentation to learn more.

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