In a command class I'm using something like this:

        $imap = @imap_open('foo', 'bar', 'baz');

        if (!$imap) {
            throw new \RuntimeException(imap_last_error());
        }

When an imap error occurs, I get an uncaught TypeError:

Uncaught TypeError: Argument 5 passed to Symfony\Component\Debug\ErrorHandler::handleError() must be of the type array, null given in /Users/gharlan/workspace/symfony_demo/vendor/symfony/symfony/src/Symfony/Component/Debug/ErrorHandler.php:368

Symfony: current master
PHP: 7.0.11

It is reproducibly with symfony demo by adding the code above to ListUsersCommand::execute: