anchor.diff:      this.animation,
       this.fit,
       this.alignment,
  +    this.placeHolder,
     }) : src = _Source.asset;
   
     const RiveAnimation.network(
  
positive.code:     this.animation,
      this.fit,
      this.alignment,
    }) : src = _Source.network;
  
    @override
  
negative.code:           fit: widget.fit,
            alignment: widget.alignment,
          )
        : widget.placeHolder ?? const SizedBox();
  }
  