Additional tests for "is defined"
Additional tests for "is defined"

- a key with value 'null' is still defined

twigjs/twig.js,justjohn/twig.js,justjohn/twig.js,twigjs/twig.js,twigjs/twig.js,dave-irvine/twig.js,dave-irvine/twig.js,justjohn/twig.js,dave-irvine/twig.js