private Occur getOccur(final ExpressionOperator operator) {
        return switch (operator.op()) {
            case OR -> Occur.SHOULD;
            case NOT -> Occur.MUST_NOT;
            default -> Occur.MUST;
        };
    }
Convert our query objects to a LUCENE query.
stroom-index/stroom-index-lucene553/src/main/java/stroom/index/lucene553/SearchExpressionQueryBuilder.java