Bogus "Conditions should not unconditionally evaluate to "TRUE" or to "FALSE"" warning

[Hixie]

This code:

enum Enum { a, b }

String test(Enum x, String s) {
  switch (x) {
    case Enum.a:
      if (s != null)
        return 'a';
      return 'b';
    case Enum.b:
      if (s != null)
        return 'c';
      return 'd';
  }
  return null;
}

void main() {
  print(test(Enum.a, ''));
}

This .analysis_options file:

linter:
  rules:
    - invariant_booleans

...results in this error:

$ dartanalyzer test.dart
Analyzing [test.dart]...
[lint] Conditions should not unconditionally evaluate to "TRUE" or to "FALSE" verify: s != null. (test.dart, line 11, col 11)
1 lint found.

[bwilkerson]

@alexeieleusis

[natebosch]

This example no longer repros for me.