presto-parser/src/main/java/io/prestosql/sql/ExpressionFormatter.java/ExpressionFormatter/visitIsNotNullPredicate
class ExpressionFormatter:        @Override
        protected String visitIsNotNullPredicate(IsNotNullPredicate node, Void context)
        {
            return "(" + process(node.getValue(), context) + " IS NOT NULL)";
        }