Invalid change using `to_type` on non-stored thing

**Describe the bug**
Using to_type on a none-stored thing generates an invalid change.

**To Reproduce**
```javascript
set_type('T', {name: 'str'});
t = {};
t.to_type('T');
t;
```
The above may create an empty change and the following should work:
```javascript
nse();
t = {};
t.to_type('T');
t;
```

**Expected behavior**
No change should be created. (`nse()` should work)
