@Test
    public final void testEmptyStructUpdate() throws IOException {
        DocumentUpdate put = parseUpdate("""
                                         {
                                           "update": "id:unittest:mirrors:g=test:whee",
                                           "create": true,
                                           "fields": {
                                             "skuggsjaa": {
                                               "assign": { }
                                             }
                                           }
                                         }
                                         """);
        assertEquals(1, put.fieldUpdates().size());
        FieldUpdate fu = put.fieldUpdates().iterator().next();
        assertEquals(1, fu.getValueUpdates().size());
        ValueUpdate vu = fu.getValueUpdate(0);
        assertTrue(vu instanceof AssignValueUpdate);
        AssignValueUpdate avu = (AssignValueUpdate) vu;
        assertTrue(avu.getValue() instanceof Struct);
        Struct s = (Struct) avu.getValue();
        assertEquals(0, s.getFieldCount());
        GrowableByteBuffer buf = new GrowableByteBuffer();
        DocumentSerializer serializer = DocumentSerializerFactory.createHead(buf);
        put.serialize(serializer);
        assertEquals(69, buf.position());
    }
Basic test of JSON streams to Vespa document instances.

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