Question about field weight value checks in CombinedFieldQuery

Hello!

I have been exploring the use of BM25F queries (CombinedFieldQuery) in
Lucene, and I have noticed that it is not allowed to use field weights with
values less than 1.0f (as shown in here:
https://github.com/apache/lucene/blob/53d1c2bd2fb3e6b9da590bee360996dbbdc8ea34/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/CombinedFieldQuery.java#L123),
in which case it will simply throw an exception.

Is there a reason why is this done? As far as my knowledge goes, there is
no reason why a BM25F field boost must be greater than 1.0 but instead
simply a positive float, or am I wrong? Instead of a boost, it would be a
penalization.

Thank you,
Samuel