anchor.diff:    /**
      * Constructor used by [CircularTypeImpl].
      */
  -  DynamicTypeImpl._circular(this.nullabilitySuffix)
  -      : super(instance.element, Keyword.DYNAMIC.lexeme);
  +  DynamicTypeImpl._circular() : super(instance.element, Keyword.DYNAMIC.lexeme);
   
     @override
     int get hashCode => 1;
   
     @override
     bool get isDynamic => true;
  +
  +  @override
  +  NullabilitySuffix get nullabilitySuffix => NullabilitySuffix.none;
   
     @override
     bool operator ==(Object object) => identical(object, this);
  
positive.code:  * `...`.
   */
  class CircularTypeImpl extends DynamicTypeImpl {
    CircularTypeImpl() : super._circular(NullabilitySuffix.star);
  
    @override
    bool operator ==(Object object) => object is CircularTypeImpl;
  
negative.code: 
    @override
    TypeImpl withNullability(NullabilitySuffix nullabilitySuffix) {
      // The void type is always nullable.
      return this;
    }
  }
  
  