I think that's why people in this thread are calling it a tradeoff. It's a very attractive option that seems like a great idea until it breaks. In happy path having default values is better, in mixed path situations, having a separate and reserved way of saying something hasn't been touched is incredibly powerful

I think default values are a major flaw, much worse than nil. An unintended default value causes data corruption. All types should be nillable in my opinion, using types that have fallback to a default value is source of nasty silent bugs. In Java for example I would never use a primitive data type.