presto-main/src/main/java/io/prestosql/cost/SymbolStatsEstimate.java/SymbolStatsEstimate/mapNullsFraction
class SymbolStatsEstimate:    public SymbolStatsEstimate mapNullsFraction(Function<Double, Double> mappingFunction)
    {
        return buildFrom(this).setNullsFraction(mappingFunction.apply(nullsFraction)).build();
    }