Undefined and null values are not properly handled

[felixlheureux]

• VS Code Version: Current
• OS Version: MacOS Ventura

Undefined and null values are not properly handled. When an undefined value is passed in Monaco, the textModel will call factory.create on an undefined value which will throw an undefined error.

Also, if a null value is passed, since the logic returns without updating the value, the previous data will still be displayed.

Solution here: microsoft/vscode#165721

Steps to Reproduce:

1. Update the data to undefined or null once the Monaco editor is already mounted.

[hediet]

Fixed with your PR. Thanks!