@Test
    public void empty_reference_field_results_in_reference_value_without_doc_id_present() throws IOException {
        final Document doc = readDocumentFromJson("id:unittest:testrefs::helloworld", "{ \"ref_field\": \"\" }");
        ReferenceFieldValue ref = (ReferenceFieldValue)doc.getFieldValue("ref_field");
        assertFalse(ref.getDocumentId().isPresent());
    }
Functional tests for com.yahoo.document.json.JsonWriter.

@author Steinar Knutsen
document/src/test/java/com/yahoo/document/json/JsonWriterTestCase.java