anchor.diff:      if (specializeClosureCall(node)) return;
   
       AbstractValue receiver = getValue(node.receiver.definition);
  -    node.receiverIsNotNull = receiver.isDefinitelyNotNull;
   
       if (node.receiverIsIntercepted &&
           node.receiver.definition.sameValue(node.arguments[0].definition)) {
  
positive.code:         CpsFragment cps = new CpsFragment(sourceInfo);
          cps.invokeBuiltin(BuiltinMethod.Push,
              list,
              <Primitive>[addedItem],
              receiverIsNotNull: listValue.isDefinitelyNotNull);
          cps.invokeContinuation(cont, [cps.makeNull()]);
          replaceSubtree(node, cps.result);
          push(cps.result);
  
negative.code:     return null;
    }
  
    Primitive visitInterceptor(Interceptor node) {
      AbstractValue value = getValue(node.input.definition);
      // If the exact class of the input is known, replace with a constant
  