public static RCOperator transform(List<ColumnSchema> schemas, List<Filter> filters) {
    List<Filter> validFilters = filters.stream().filter(f -> !(f instanceof IsNotNull)).collect(Collectors.toList());
    if (validFilters.size() == 0) {
        return null;
    }
    RCOperator op = new io.indexr.segment.rc.And(Trick.mapToList(validFilters, f -> transform(schemas, f)));
    op = op.optimize();
    return op;
}