As a workaround, I went without the check and just parameter('param'), doing the check somewhere else.

@Stelian You could do this in the Bundle (Dependency Injection) Extension of your bundle.

@hacfi, totally true, can even be solved in the a compiler pass, but it's pretty much a 1 to 1 use case as described in the docs here: http://symfony.com/doc/current/book/service_container.html#using-the-expression-language.

This is pretty much the reason for opening the issue.

@Stelian Sorry..wasn’t aware of that as I haven’t spent much time using the Expression Language.

Actually, I'm not sure if this ever worked. Looks like it has been broken before the ExpressionLanguage component was merged (when this was replaced with container in 984bd38).

What you can do in a PR for: https://github.com/symfony/symfony/blob/master/src/Symfony/Component/DependencyInjection/ExpressionLanguage.php

// add this code in the registerFunctions()
$this->register('has_parameter', function ($arg) {
    return sprintf('$this->hasParameter(%s)', $arg);
}, function (array $variables, $value) {
    return $variables['container']->hasParameter($value);
});

I'm not sure if this would be desired, but it's an option. If you make a PR with this code, you should update the docs too.

This would allow:

has_parameter('param') ? parameter('param') : 'null'

#12030 should fix the problem. Can you confirm?

@fabpot, yes it works with your commit, thank you.