anchor.diff:          && darkColor != null
           && textColor != null
           && style != null
  +        && margin != null
           && _position != null
           && _position.isFinite
           && _opacity != null
           && _opacity >= 0.0
  -        && _opacity <= 1.0
  -        && margin != null);
  +        && _opacity <= 1.0);
       return true;
     }
   
  
positive.code:       Color.lerp(a.darkColor, b.darkColor, t),
        Color.lerp(a.textColor, b.textColor, t),
        t < 0.5 ? a.style : b.style,
        a._position + (b._position - a._position) * t,
        (a._opacity + (b._opacity - a._opacity) * t).clamp(0.0, 1.0),
        EdgeInsets.lerp(a.margin, b.margin, t),
      );
    }
  
  
negative.code:   /// controls whether and where to draw the "Flutter" label. If one is shown,
    /// the [textColor] controls the color of the label.
    ///
    /// The [lightColor], [darkColor], [textColor], [style], and [margin]
    /// arguments must not be null.
    const FlutterLogoDecoration({
      this.lightColor: const Color(0xFF42A5F5), // Colors.blue[400]
      this.darkColor: const Color(0xFF0D47A1), // Colors.blue[900]
      this.textColor: const Color(0xFF616161),
      this.style: FlutterLogoStyle.markOnly,
      this.margin: EdgeInsets.zero,
    }) : assert(lightColor != null),
         assert(darkColor != null),
         assert(textColor != null),
         assert(style != null),
         assert(margin != null),
         _position = style == FlutterLogoStyle.markOnly ? 0.0 : style == FlutterLogoStyle.horizontal ? 1.0 : -1.0, // ignore: CONST_EVAL_TYPE_BOOL_NUM_STRING
         // (see https://github.com/dart-lang/sdk/issues/26980 for details about that ignore statement)
         _opacity = 1.0;
  
    const FlutterLogoDecoration._(this.lightColor, this.darkColor, this.textColor, this.style, this.margin, this._position, this._opacity);
  
    /// The lighter of the two colors used to paint the logo.
    ///
  