anchor.diff:    bool get isWheelEvent => this.tryCast<SyntheticWheelEvent>() != null;
   }
   
  -
  -class SyntheticEventHelper {
  -  static SyntheticEvent getEmptyEvent() => SyntheticEvent(null, null, null, null, null, () {}, null, null, null, null, 0, 'empty event');
  +class _SyntheticEventHelper {
  +  static SyntheticEvent getEmptyEvent() => SyntheticEvent(null, null, null, null, () {}, () {}, null, null, null, null, 0, 'empty event');
     static SyntheticClipboardEvent getEmptyClipboardEvent() => SyntheticClipboardEvent(null, null, null, null, () {}, () {}, null, null, null, null, 0, 'empty event', null);
     static SyntheticKeyboardEvent getEmptyKeyboardEvent() => SyntheticKeyboardEvent(null, null, null, null, () {}, () {}, null, null, null, null, 0, null, null, null, null, null, null, null, null, null, null, null, null);
     static SyntheticCompositionEvent getEmptyCompositionEvent() => SyntheticCompositionEvent(null, null, null, null, () {}, () {}, null, null, null, null, 0, 'empty event', null);
  
positive.code:   static SyntheticUIEvent getEmptyUIEvent() => SyntheticUIEvent(null, null, null, null, () {}, () {}, null, null, null, null, 0, 'empty event', null, null);
    static SyntheticWheelEvent getEmptyWheelEvent() => SyntheticWheelEvent(null, null, null, null, () {}, () {}, null, null, null, null, 0, 'empty event', null, null, null, null);
  
  
  
  
  
  }
  
  
  
  // A temporary measure that will be removed when Duck typing is added
  // in the React 17 release branch.
  
negative.code: import '../../react.dart';
  
  SyntheticEvent getEmptySyntheticEvent() => _SyntheticEventHelper.getEmptyEvent();
  SyntheticClipboardEvent getEmptyClipboardEvent() => _SyntheticEventHelper.getEmptyClipboardEvent();
  SyntheticKeyboardEvent getEmptyKeyboardEvent() => _SyntheticEventHelper.getEmptyKeyboardEvent();
  SyntheticCompositionEvent getEmptyCompositionEvent() => _SyntheticEventHelper.getEmptyCompositionEvent();
  SyntheticFocusEvent getEmptyFocusEvent() => _SyntheticEventHelper.getEmptyFocusEvent();
  SyntheticFormEvent getEmptyFormEvent() => _SyntheticEventHelper.getEmptyFormEvent();
  SyntheticMouseEvent getEmptyMouseEvent() => _SyntheticEventHelper.getEmptyMouseEvent();
  SyntheticPointerEvent getEmptyPointerEvent() => _SyntheticEventHelper.getEmptyPointerEvent();
  SyntheticTouchEvent getEmptyTouchEvent() => _SyntheticEventHelper.getEmptyTouchEvent();
  SyntheticAnimationEvent getEmptyAnimationEvent() => _SyntheticEventHelper.getEmptyAnimationEvent();
  SyntheticUIEvent getEmptyUIEvent() => _SyntheticEventHelper.getEmptyUIEvent();
  SyntheticWheelEvent getEmptyWheelEvent() => _SyntheticEventHelper.getEmptyWheelEvent();
  
  SyntheticEvent buildSyntheticEvent({SyntheticWheelEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildEvent(baseEvent, newEventProperties);
  SyntheticClipboardEvent buildClipboardEvent({SyntheticClipboardEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildClipboardEvent(baseEvent, newEventProperties);
  SyntheticKeyboardEvent buildKeyboardEvent({SyntheticKeyboardEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildKeyboardEvent(baseEvent, newEventProperties);
  SyntheticCompositionEvent buildCompositionEvent({SyntheticCompositionEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildCompositionEvent(baseEvent, newEventProperties);
  SyntheticFocusEvent buildFocusEvent({SyntheticFocusEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildFocusEvent(baseEvent, newEventProperties);
  SyntheticFormEvent buildFormEvent({SyntheticFormEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildFormEvent(baseEvent, newEventProperties);
  SyntheticMouseEvent buildMouseEvent({SyntheticMouseEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildMouseEvent(baseEvent, newEventProperties);
  SyntheticPointerEvent buildPointerEvent({SyntheticPointerEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildPointerEvent(baseEvent, newEventProperties);
  SyntheticTouchEvent buildTouchEvent({SyntheticTouchEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildTouchEvent(baseEvent, newEventProperties);
  SyntheticAnimationEvent buildAnimationEvent({SyntheticAnimationEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildAnimationEvent(baseEvent, newEventProperties);
  SyntheticUIEvent buildUIEvent({SyntheticUIEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildUIEvent(baseEvent, newEventProperties);
  SyntheticWheelEvent buildWheelEvent({SyntheticWheelEvent baseEvent, Map<String, dynamic> newEventProperties}) => _SyntheticEventHelper.buildWheelEvent(baseEvent, newEventProperties);
  
  extension SyntheticEventTypeHelpers on SyntheticEvent {
    bool get isClipboardEvent => this.tryCast<SyntheticClipboardEvent>() != null;
  