anchor.diff:        Iterable<String> returnsAnnotations, TypeLookup lookupType) {
       if (createsAnnotations.isEmpty && returnsAnnotations.isEmpty) return;
   
  -    List<Object> creates = _collect(createsAnnotations, lookupType);
  -    List<Object> returns = _collect(returnsAnnotations, lookupType);
  +    List<Object>? creates = _collect(createsAnnotations, lookupType);
  +    List<Object>? returns = _collect(returnsAnnotations, lookupType);
   
       if (creates != null) {
         _behavior.typesInstantiated
  
positive.code:       Iterable<String> createAnnotations,
        Iterable<String> returnsAnnotations,
        TypeLookup lookupType,
        {bool isJsInterop}) {
      _behavior = NativeBehavior();
      DartType returnType = type.returnType;
      // Note: For dart:html and other internal libraries we maintain, we can
  
negative.code:       });
      }
  
      String? creates = values['creates'];
      if (creates != null) {
        resolveTypesString(dartTypes, creates, onVoid: () {
          reportError("Invalid type string 'creates:$creates'");
  