anchor.diff:      }
   
       bool hasFreeFormal(t) {
  +      // Ignore nullability wrappers.
  +      if (_isLegacy(t) || _isNullable(t)) {
  +        return hasFreeFormal(JS<Type>('', '#.type', t));
  +      }
         if (partials.containsKey(t)) return true;
         // Generic classes and typedefs.
         var typeArgs = getGenericArgs(t);
  
positive.code:   Type get runtimeType => Type;
  }
  
  /// Given an internal runtime type object, wraps it in a `_Type` object
  /// that implements the dart:core Type interface.
  Type wrapType(type) => _wrapType(type, false);
  
  /// Helper function to wrap a type.
  ///
  /// When isNormalized is true, the parameter is known to be in a canonicalized
  /// normal form, so the algorithm can directly wrap and return the value.
  Type _wrapType(type, isNormalized) {
    // If we've already wrapped this type once, use the previous wrapper. This
    // way, multiple references to the same type return an identical Type.
    if (JS('!', '#.hasOwnProperty(#)', type, _typeObject)) {
  
negative.code:   }
  
    return null;
  }