public RelNode convert(RelNode rel) { final LogicalCalc calc = (LogicalCalc) rel; if (RexMultisetUtil.containsMultiset(calc.getProgram())) { return null; } return new MongoCalcRel( rel.getCluster(), rel.getTraitSet().replace(out), convert( calc.getChild(), calc.getTraitSet().replace(out)), calc.getProgram(), Project.Flags.Boxed); }