This issue was originally filed by [email protected]

foo([x]) {
  print('x = $x');
}

main() {
  foo();
}

In Dartboard leads to:

NoSuchMethodException - receiver: '' function name: '' arguments: []]

In DartVM works fine (output 'x = null')

The holy spec is somewhat unclear on the subj, but "6.2.2 Named Optional Formals" marks default value for optional argument optional, so DartVM behaviour seems reasonable.