Complete future with an error.
Calling complete or completeError must be done at most once.
Completing a future with an error indicates that an exception was thrown while trying to produce a value.
null, it is replaced by a NullThrownError.
error is a
Future, the future itself is used as the error value.
If you want to complete with the result of the future, you can use:
or if you only want to handle an error from the future:
void completeError(Object error, [StackTrace stackTrace]);