fix null pointer exception when ancestry is empty

This MR fixes a subtle null pointer exception which could occur in the follow line: !record.getAncestry().getParents().isEmpty()) when the ancestry has no parent. The getParents() would return null. The next call isEmpty() would cause a null pointer exception when called on the returned null parents object.

The fix is to replace the line with the following line: !Collections.isEmpty(record.getAncestry().getParents())) Now if the getParents() method returns null, the Collections.isEmpty(null) call will correctly return true instead of null pointer exception as expected.

Corresponding unit tests have been updated accordingly.