anchor.diff:  
     @patch
     @pragma("vm:prefer-inline")
  -  factory Float64x2.splat(double v) => _Float64x2Splat(v);
  +  factory Float64x2.splat(double v) {
  +    _throwIfNull(v, 'v');
  +    return _Float64x2Splat(v);
  +  }
   
     @pragma("vm:exact-result-type", _Float64x2)
     static _Float64x2 _Float64x2Splat(double v) native "Float64x2_splat";
  
positive.code: 
    @patch
    @pragma("vm:prefer-inline")
    factory Float32x4.splat(double v) => _Float32x4Splat(v);
  
    @pragma("vm:exact-result-type", _Float32x4)
    static _Float32x4 _Float32x4Splat(double v) native "Float32x4_splat";
  
negative.code: class Float64x2 {
    @patch
    @pragma("vm:prefer-inline")
    factory Float64x2(double x, double y) {
      _throwIfNull(x, 'x');
      _throwIfNull(y, 'y');
      return _Float64x2FromDoubles(x, y);
    }
  
    @pragma("vm:exact-result-type", _Float64x2)
    static _Float64x2 _Float64x2FromDoubles(double x, double y)
  