Can't use %paths.base% inside extensions: Failed opening required '%paths.base%' about behat

[tomasvts]

Related
FriendsOfBehat/SymfonyExtension#151

[tomasvts]

Update:
The variable expansion works outside the "extensions" block.
So if I remove paths.base from the extensions block it works:

default:
    gherkin:
        filters:
            tags: ~oauth
    calls:
        error_reporting: 16383 # E_ALL & ~E_USER_DEPRECATED
    autoload:
        '': '%paths.base%/tests/Functional/Bootstrap'
    extensions:
        FriendsOfBehat\SymfonyExtension:
            bootstrap: /full/path/to/my/workspace/folder/tests/bootstrap.php
        rdx\behatvars\BehatVariablesExtension: ~
    suites:
        default:
            paths:
                - '%paths.base%/tests/Functional/Features'
            contexts:
                - rdx\behatvars\BehatVariablesContext
                - App\Tests\Functional\Bootstrap\SetupContext:
                - App\Tests\Functional\Bootstrap\HttpContext: