setting rust-analyzer.server.extraEnv.key = null crashes the TS extension

[jyn514]

rust-analyzer version: rust-analyzer version: 0.3.2379-standalone (8365cf8 2025-04-13) [/home/jyn/.vscode/extensions/rust-lang.rust-analyzer-0.3.2379-linux-x64/server/rust-analyzer]

rustc version (eg. output of rustc -V): rustc 1.88.0-nightly (78f2104e3 2025-04-16)

editor or extension: VSCode 1.96.2 (fabdb6a30b49f79a7aba0f2ad9df9b399473380f), extension version 0.3.2379

relevant settings:

$ cat .vscode/settings.json
{
    "rust-analyzer.server.extraEnv": {
        "ENV": null
    }
}

2025-04-19 09:18:41.267 [error] Bootstrap error TypeError: Cannot read properties of null (reading 'toString')
	at /home/jyn/.vscode/extensions/rust-lang.rust-analyzer-0.3.2379-linux-x64/out/main.js:48:4821
	at Array.map (<anonymous>)
	at get serverExtraEnv (/home/jyn/.vscode/extensions/rust-lang.rust-analyzer-0.3.2379-linux-x64/out/main.js:48:4784)

found while investigating #19626

[Veykril]

Needs a null / undefined check here

rust-analyzer/editors/code/src/config.ts

Line 221 in a09a550

typeof v !== "string" ? v.toString() : v,

and corresponding type adjustments