presto-main/src/main/java/io/prestosql/sql/relational/SqlToRowExpressionTranslator.java/SqlToRowExpressionTranslator/visitIsNullPredicate
class SqlToRowExpressionTranslator:        @Override
        protected RowExpression visitIsNullPredicate(IsNullPredicate node, Void context)
        {
            RowExpression expression = process(node.getValue(), context);

            return new SpecialForm(IS_NULL, BOOLEAN, expression);
        }