toString() on null can end up printing 'undefined'

[dgrove]

@r1867

cloned from issue #67 (originally filed for dartc) for frog:

foo([x]) {
  print('x = $x');
}

main() {
  foo();
}

Frog outputs: 'x = undefined'
In DartVM works fine (output 'x = null')

[jmesserly]

as mentioned in http://code.google.com/p/dart/issues/detail?id=595:

Regarding the toString issue--I'm not sure what to do there. We either need to give up on undefined being a synonym for null, or generate uglier string interp/concat and toString code.

[jmesserly]

(updated title)

Also, btw, there's a related issue--I think "null.toString()" throws an error, instead of returning "null"

---

Changed the title to: "toString() on null can end up printing 'undefined'".

[anders-sandholm]

Removed Area-Frog label.
Added Area-Dart2JS, FromAreaFrog labels.

[kasperl]

Added WontFix label.