presto-main/src/main/java/io/prestosql/cost/FilterStatsCalculator.java/FilterExpressionStatsCalculatingVisitor/visitIsNotNullPredicate
class FilterExpressionStatsCalculatingVisitor:        @Override
        protected PlanNodeStatsEstimate visitIsNotNullPredicate(IsNotNullPredicate node, Void context)
        {
            if (node.getValue() instanceof SymbolReference) {
                Symbol symbol = Symbol.from(node.getValue());
                SymbolStatsEstimate symbolStats = input.getSymbolStatistics(symbol);
                PlanNodeStatsEstimate.Builder result = PlanNodeStatsEstimate.buildFrom(input);
                result.setOutputRowCount(input.getOutputRowCount() * (1 - symbolStats.getNullsFraction()));
                result.addSymbolStatistics(symbol, symbolStats.mapNullsFraction(x -> 0.0));
                return result.build();
            }
            return PlanNodeStatsEstimate.unknown();
        }