I wonder if this supports a cleaner way to throw when the target property's parent object is null? With null-coalescing assignment, you can do the following which will throw when 'x' is null:

  string x = null;
  string y = x ?? throw new ArgumentException("x is null");

It would be interesting to try something like:

  customer?.Name = newName ?? throw new InvalidOperationException("customer is null");

But I don't know how the language would be able to determine which potential null it was throwing for: 'customer' could be null, but so could 'newName'. I guess... maybe you could do:

  (customer ?? throw new InvalidOperationException("customer is null")).Name = newName ?? throw new ArgumentException("newName is null");

But the language already supports that, and it's extremely ugly...