anchor.diff:      }
       return _convertNullability(
           _dartTypes.typeVariableType(elementMap.getTypeVariable(node.parameter)),
  -        node.nullability);
  +        node);
     }
   
     @override
  
positive.code: 
    DartTypes get _dartTypes => elementMap.commonElements.dartTypes;
  
    DartType _convertNullability(DartType baseType, ir.Nullability nullability) {
      switch (nullability) {
        case ir.Nullability.nullable:
          return _dartTypes.nullableType(baseType);
        case ir.Nullability.legacy:
          return _dartTypes.legacyType(baseType);
        default:
          return baseType;
      }
    }
  
    DartType visitType(ir.DartType type) {
  
negative.code:   DartType visitTypeParameterType(ir.TypeParameterType node) {
      DartType typeParameter = currentFunctionTypeParameters[node.parameter];
      if (typeParameter != null) {
        return _convertNullability(typeParameter, node);
      }
      if (node.parameter.parent is ir.Typedef) {
        // Typedefs are only used in type literals so we never need their type
  