anchor.diff:          promoteTypeParameter(T, numNone),
         ),
         strT0: 'Null?',
  -      strT1: 'T, T & num',
  +      strT1: 'T, T extends Object?, T & num',
       );
     }
   
  
positive.code:     isNotSubtype(
        typeParameterTypeNone(T),
        nullQuestion,
        strT0: 'T',
        strT1: 'Null?',
      );
    }
  
negative.code:     isSubtype(
        typeParameterTypeStar(S),
        numStar,
        strT0: 'S*, S extends num*',
        strT1: 'num*',
      );
    }
  