NNBD. No error in VM if optional non-nullable parameter has no default value

[sgrekhov]

According to the NNBD specification

It is an error if an optional parameter (named or otherwise) with no default value has a potentially non-nullable type except in the parameter list of an abstract method declaration.

In fact, analyzer reports this error but VM doesn't. For example, the following code works in VM without any error

class A {}

class C {
  static void test1(var v, [A a]) {}
//                            ^
// [analyzer] unspecified
// [cfe] unspecified

  static void test2(var v, {A a}) {}
//                            ^
// [analyzer] unspecified
// [cfe] unspecified

  void test11(var v, [A a]) {}
//                      ^
// [analyzer] unspecified
// [cfe] unspecified

  void test22(var v, {A a}) {}
//                      ^
// [analyzer] unspecified
// [cfe] unspecified
}

void test1(var v, [A a]) {}
//                   ^
// [analyzer] unspecified
// [cfe] unspecified

void test2(var v, {A a}) {}
//                   ^
// [analyzer] unspecified
// [cfe] unspecified

main() {
}

Dart VM version: 2.8.0-dev.12.0 (Thu Mar 5 11:45:50 2020 +0100) on "windows_x64"

[a-siva]

I believe this needs the --force-nnbd-checks guard in CFE to be removed which is tracked in #40980.
This issue can be closed a dup of that issue.