Reference lookup query fails for empty `@DocumentReference` `List` and `Map`

[Izimbergenov]

Hello,

I have a problem when using @DocumentReference with an empty list. Specifically when we initialize our list as new ArrayList<>(). Below are the test codes: the first one failed, the second one success

static class Book
{
	@MongoId(targetType = FieldType.OBJECT_ID)
	String id;

	String name;
}

static class Library
{
	@MongoId(targetType = FieldType.OBJECT_ID)
	String id;

	@DocumentReference
	private List<Book> books = new ArrayList<>();
}

Failed test code(throws NoSuchElementException when template.findById):

@Test
public void Given_Library_Without_Books_When_Get_By_Id_Then_Success() throws Exception
{
	Library library = new Library();
	library = template.save(library);

	Library existingLibrary = template.findById(library.id, Library.class);
	assertThat(existingLibrary).isNotNull();
}

Success test code:

@Test
public void Given_Library_With_Books_When_Get_By_Id_Then_Success() throws Exception
{
	Book book = new Book();
	book.name = "Harry Potter";
	book = template.save(book);

	Library library = new Library();
	library.books = Arrays.asList(book);
	library = template.save(library);

	Library existingLibrary = template.findById(library.id, Library.class);
	assertThat(existingLibrary).isNotNull();
}

Spring Data MongoDB version: 3.3.0-SNAPSHOT

[christophstrobl]

Thanks for reporting - we'll look into it.