public Object get(String collection, String referenceElementId) {
        if (collectionRegistry.containsKey(collection)) {
            return collectionRegistry.get(collection).get(referenceElementId);
        }
        return null;
    }
@Test
    public void shouldReturnNullReferenceElementWhenCollectionIsMissing(){
        ConfigReferenceElements configReferenceElements = new ConfigReferenceElements();
        assertThat(configReferenceElements.get("missing-collection", "id"), is(nullValue()));
    }