anchor.diff:    }
   
     void visitGetField(GetField node) {
  +    node.objectIsNotNull = getValue(node.object.definition).isDefinitelyNotNull;
       setValue(node, nonConstant(typeSystem.getFieldType(node.field)));
     }
   
  
positive.code:   @override
    void visitGetLength(GetLength node) {
      AbstractValue input = getValue(node.object.definition);
      int length = typeSystem.getContainerLength(input.type);
      if (length != null) {
        // TODO(asgerf): Constant-folding the length might degrade the VM's
  
negative.code: 
    void visitInvokeMethod(InvokeMethod node) {
      AbstractValue receiver = getValue(node.receiver.definition);
      node.receiverIsNotNull = receiver.isDefinitelyNotNull;
      if (receiver.isNothing) {
        return;  // And come back later.
      }
  