Removing an item

How can I remove an item? If I just remove it from the `List` it triggers this error:
```
══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following IndexError was thrown building:
RangeError (index): Index out of range: index must not be negative: -1
```

No file or test is named. Start by reproducing the error when an item is removed from the List, then trace the widget implementation to the code handling list changes and the reported negative index. Done means removing an item no longer throws the shown RangeError.

Written by the indexing model from the issue text.