Future can't be completed with null exception

[DartBot]

This issue was originally filed by [email protected]

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What steps will reproduce the problem?
Run the following test:

main() {
  var completer = new Completer();
  var future = completer.future;
  completer.completeException(null);
  print(future.exception);
}

What is the expected output? What do you see instead?
Documentation does not prohibit from passing null, so expected output is 'null'.
Actual: IllegalArgumentException is thrown.

What version of the product are you using? On what operating system?
DartVM, Frog r4736. OS Ubuntu 10.04.

Please provide any additional information below.

[kasperl]

Set owner to @sigmundch.
Added Area-Language, Triaged labels.

[sigmundch]

I'll update the documentation to keep the current semantics (IllegalArgumentException).

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Added Accepted label.

[sigmundch]

Added Fixed label.