private static List<Expression> filterList(Iterable<Expression> list) {
        List<Expression> filtered = new ArrayList<>();
        for (Expression expression : list) {
            if (expression instanceof StatementExpression statement) {
                filtered.addAll(filterList(statement));
            } else if (expression != null) {
                filtered.add(expression);
            }
        }
        return filtered;
    }
Creates an expression with simple lingustics for testing
indexinglanguage/src/main/java/com/yahoo/vespa/indexinglanguage/expressions/StatementExpression.java