presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/TransformCorrelatedInPredicateToJoin.java/TransformCorrelatedInPredicateToJoin/isNotNull
class TransformCorrelatedInPredicateToJoin:    private static Expression isNotNull(Symbol symbol)
    {
        return new IsNotNullPredicate(symbol.toSymbolReference());
    }