presto-main/src/main/java/io/prestosql/sql/planner/DomainTranslator.java/Visitor/visitIsNotNullPredicate
class Visitor:        @Override
        protected ExtractionResult visitIsNotNullPredicate(IsNotNullPredicate node, Boolean complement)
        {
            if (!(node.getValue() instanceof SymbolReference)) {
                return super.visitIsNotNullPredicate(node, complement);
            }

            Symbol symbol = Symbol.from(node.getValue());
            Type columnType = checkedTypeLookup(symbol);

            Domain domain = complementIfNecessary(Domain.notNull(columnType), complement);
            return new ExtractionResult(
                    TupleDomain.withColumnDomains(ImmutableMap.of(symbol, domain)),
                    TRUE_LITERAL);
        }