Forgot that missing environment variables are replaced with empty string.

Fixes #4895

- Listen to model added/removed changes to start/stop watching the file
- Clean up and simplify implementation

Fixes #37858

Part of #37858

* SelectBox drop-down-contextv-list WIP 1

* Merge 2

* Selectbox Themed drop-down

* Added ARIA labels, color cleanup

* Restored Space and Enter select activation

* Fix list colors, CSS, Scrollbar, hover before separation

* SelectBox separation, clean 1

* SelectBox separation cleanup 2

* SelectBox fix var, superfluous listener

* some final polish

* actually import the CSS

* Require to use "-" when reading from stdin

* cli - better help message

* more narrow error handling

* better data listener

Fixes #34193