Yea, I meant the ability to declare functions that only accept non-nullable args. For ex: You have a chain of function calls, A -> B -> C -> D, where B, C, and D only accept a non-nullable arg then you can save the mental load of checking for null in 3 functions. Only A would need to check the var for null before calling B with that var.

The safety is contagious, preventing crashes from nil pointer dereferences at runtime. For ex: 99% of your program is functions accepting only non-nullable types then 99% of your program is guaranteed to not crash from nil pointer deref.

With Go, you have to check for nil in every function even if all your callers already check for nil. That's because Go can't declare a function's arg as non-nullable type.