}
@Test
public void testSysObjectReferenceNull() throws Exception {
NullFieldSysObjectReference nullRef = new NullFieldSysObjectReference();
SysExpression n = nullRef.getChildImplementation("n");
assertThat(n, instanceOf(BytesRefNullSysExpression.class));
Map<String, Object> value = nullRef.value();
assertThat(value.size(), is(1));
assertThat(value, hasKey("n"));