protected Query le(Operation<?> operation, QueryMetadata metadata) {
        verifyArguments(operation);
        Path<?> path = getPath(operation.getArg(0));
        return range(path, toField(path), null, operation.getArg(1), true,
                true, metadata);
    }
If the query is a BooleanQuery and it contains a single Occur.MUST_NOT
clause it will be returned as is. Otherwise it will be wrapped in a
BooleanClause with the given Occur.
querydsl-lucene5/src/main/java/com/querydsl/lucene5/LuceneSerializer.java