Found the answer myself onĀ https://www.monetdb.org/wiki/MonetDB_type_system

Character \200 works to indicate a real NULL in MonetDB.

Best regards,
Dennis

On Fri, Sep 23, 2016 at 5:05 PM, Dennis Pallett <dennis@pallett.nl> wrote:
Hi all,

I'm working on a utility to bulk load data into MonetDB using the binary bulk loading options. At the moment I'm running into the issue whereby I'm unable to insert real NULL values in varchar columns. Only a literal "null" is inserted, which obviously fails the 'WHERE col IS NULL' condition. Can anyone tell me what value is used to import a null value into a varchar column?

Best regards,
Dennis