handleKeyData method Null safety

Implementation

bool handleKeyData(ui.KeyData data) {
  _transitMode ??= KeyDataTransitMode.keyDataThenRawKeyData;
  switch (_transitMode!) {
    case KeyDataTransitMode.rawKeyData:
      assert(false, 'Should never encounter KeyData when transitMode is rawKeyData.');
      return false;
    case KeyDataTransitMode.keyDataThenRawKeyData:
      // Having 0 as the physical and logical ID indicates an empty key data
      // (the only occassion either field can be 0,) transmitted to ensure
      // that the transit mode is correctly inferred. These events should be
      // ignored.
      if (data.physical == 0 && data.logical == 0) {
        return false;
      }
      assert(data.physical != 0 && data.logical != 0);
      final KeyEvent event = _eventFromData(data);
      if (data.synthesized && _keyEventsSinceLastMessage.isEmpty) {
        // Dispatch the event instantly if both conditions are met:
        //
        // - The event is synthesized, therefore the result does not matter.
        // - The current queue is empty, therefore the order does not matter.
        //
        // This allows solitary synthesized `KeyEvent`s to be dispatched,
        // since they won't be followed by `RawKeyEvent`s.
        _hardwareKeyboard.handleKeyEvent(event);
        _dispatchKeyMessage(<KeyEvent>[event], null);
      } else {
        // Otherwise, postpone key event dispatching until the next raw
        // event. Normal key presses always send 0 or more `KeyEvent`s first,
        // then 1 `RawKeyEvent`.
        _keyEventsSinceLastMessage.add(event);
      }
      return false;
  }
}