Fairly sure this is a "your (or your counterparty's) bank is broken" thing, not a "SWIFT is broken" thing. ISO 15022 (as used here) and ISO 20022 (as used by fancy modern banks who are willing to get onboard with a message format a mere 20 years old) will handle the string 'null' just fine. ISO 15022 doesn't, IIRC, really have a way to represent null the concept at all; you just wouldn't provide the relevant field.

At a guess, the message parsing by the receiving bank is likely to be broken.

It's a fascinating edge case, but also feels like a silly choice of company name for this exact reason.

What other systems are going to shut you out for your choice of company name?

It's good to see that Bobby Tables is doing well and started a business.

I’m sorry this happened to you, but come on. You could have called your company Not Available or named your painting Untitled or your son Deceased Stillbirth and run the risk of miscommunication.