presto-parser/src/main/java/io/prestosql/sql/ExpressionFormatter.java/ExpressionFormatter/visitNullIfExpression
class ExpressionFormatter:        @Override
        protected String visitNullIfExpression(NullIfExpression node, Void context)
        {
            return "NULLIF(" + process(node.getFirst(), context) + ", " + process(node.getSecond(), context) + ')';
        }