To reproduce, in Squeak, do this:

```smalltalk 'aaa' copy tryPrimitive: 64 withArgs: {2. $b asciiValue}; yourself ```

Expected behavior: The primitive fails, and the string remains `aaa`. This is also what we are used to from primitive 61 (primitiveAtPut).

Actual behavior: The primitive fails, but the string slot has been changed to `Character null`.

(By the way, TruffleSqueak and SqueakJS show my expected behavior.)

Maybe there is some clever reasoning behind it, but a primitive that fails should not have any other side effects from my first impression. Is this a bug?