Make the behavior of an empty query configurable in `QueryParser`

[fulmicoton]

In some use case, most of the time, people want an empty query to match nothing, but for some analytics use case, it might make more sense for empty query to match all documents.

Add a setter ".set_empty_query_match_all(should_match_all: bool)" to the QueryParser to enforce the non default behavior.
(Also add a getter .get_empty_query_match_all() to read this property).

[druzn3k]

Ok @fulmicoton , I wrote the code for this issue, but I need a little help on writing the tests. Could you help me?

[fulmicoton]

For the unit tests, I think you can work from the logical ast.

Make tests on what you get when you call

query_parser.parse_query_to_logical_ast("")
query_parser.parse_query_to_logical_ast("   ")

depending on whether query_parser.set_empty_query_match_all() was called or not.

[druzn3k]

Thanks 👍

[druzn3k]

Ok, I wrote the PR. Is far from perfect (IMHO), but it can get an eventual discussion started. I can for sure expand (if needed) the test suite. Let me know, I'm really interested in knowing if there is any issue.

Thanks! 💯