assertProblemFree(collector);

        assertEquals("${env.DOES_NOT_EXIST}", out.getProperties().get("outputDirectory"));
    }

    @Test
    public void expressionThatEvaluatesToNullReturnsTheLiteralString() throws Exception {
        Map<String, String> modelProperties = new HashMap<>();
        modelProperties.put("outputDirectory", "${DOES_NOT_EXIST}");