Issue 34 - Query for property directly on an array should throw InvalidPathException instead of returning null

Current behavior is to return 'null' in this case. Looking at  Issue 7  it appears this was intentional.

However, it is confusing because 'null' is a valid json value... So it looks like the key has a field 'invalid', and the value was 'null', when actually no such field exists.

I would expect an InvalidPathException, which is what is thrown elsewhere when queries are made for fields that do not exist.